Oceans doi: 10.3390/oceans6010005

Authors: Noelle Lucey Carolina César-Ávila Alaina Eckert Paul Veintimilla Rachel Collin

One approach to improve long-term coral restoration success utilizes naturally stress-tolerant corals from the wild. While the focus has primarily been on thermal stress, low oxygen is a growing threat to coral reefs and restoration efforts should also consider hypoxia tolerance. Here we determine if Siderastrea siderea and Agaricia tenuifolia populations from a reef with a historical record of low oxygen exhibit evidence of local adaptation to hypoxic events, compared to populations from a reference reef. We employed a laboratory-based reciprocal transplant experiment mimicking a severe 14-night hypoxic event and monitored bleaching responses, photo-physiology, metabolic rates, and survival of all four populations during, and for two weeks following the event. In both species, we found the populations from the hypoxic reef either fully persisted or recovered within 3 days of the event. In contrast, the conspecific naïve populations from the well-oxygenated reference reef experienced bleaching and death. This showcases the vulnerability of naïve corals exposed to low oxygen but also suggests that corals from the hypoxic reef locally adapted to survive severe episodic hypoxia. Other reefs with past episodic low oxygen may also be home to corals with adaptation signatures to hypoxia and may be useful for restoration efforts.

Oceans doi: 10.3390/oceans6010004

Authors: Victor Garcia-Bustos

The Mediterranean Sea, a global biodiversity hotspot, faces significant threats that compromise its ecological health. While Marine Protected Areas (MPAs) play a crucial role in biodiversity conservation, their effectiveness is debated, and empirical data on their impact remain limited. This study evaluates the utility of Local Ecological Knowledge (LEK) from divers along the Spanish Mediterranean coast to assess perceived abundance of sentinel species in both MPAs and non-protected areas, in relation to empirical data, alongside divers’ attitudes toward ocean threats and conservation strategies. Divers perceived higher abundance and subjective health indicators of key species, such as Posidonia oceanica, octocorals, and top predators within MPAs, which aligns with empirical evidence supporting MPA effectiveness in conserving biodiversity and mitigating human disturbances. Notably, divers showed knowledge gaps, particularly underestimating climate change impacts while overemphasizing pollution threats. Diver education emerged as a critical factor in shaping conservation attitudes, with higher education levels correlating with increased environmental awareness and stronger support for conservation measures. This study underscores the potential of leveraging LEK in marine conservation strategies while acknowledging limitations related to self-reported data and regional specificity, advocating for expanded geographic scope and integration with empirical data in future research.

Oceans doi: 10.3390/oceans6010003

Authors: Benedict C. Posadas

Impact assessments are necessary for supporting fisheries’ disaster applications and management options for states affected by disasters. This paper measures the joint and individual impacts of man-made and natural disasters, global pandemics and recessions, the U.S.-China trade war, and recent increases in fuel prices on commercial dockside values of the Mississippi blue crab fishery. The mean-difference model estimates the direct impacts when the current dockside values fall below the benchmark values. The marine economic recovery model identifies the significant determinants of the variations in the dockside values. Mean-difference model results indicate that the Mississippi blue crab fishery sustained direct losses due to Hurricane Katrina in 2005, the Deepwater Horizon oil spill in 2010, and the opening of the Bonnet Carre Spillway in 2011. The estimated marine economic recovery model explained 93 percent of the variations in real dockside values. Two independent variables are statistically significant, including blue crab landings and time. The disaster variables have the expected signs but are not statistically significant. These methodologies’ usefulness is applicable in assessing the direct impacts on fisheries and other economic sectors affected by disasters such as major hurricanes, oil spills, massive freshwater intrusion, and harmful algal blooms.

Oceans doi: 10.3390/oceans6010002

Authors: Richard M. Warwick James R. Tweedley Michael Camplin Blaise Bullimore

This study determined the environmental condition of the benthos of Milford Haven Waterway, an area that is arguably the most vulnerable in the UK to anthropogenic activities, including the potential effects of a major oil spill in 1996, using historical data on the macrobenthos more than a decade later in 2008, 2010 and 2013. These data show a gradual decline in numerous univariate diversity measures from the outer (marine) to inner (estuarine) stations. Taxonomic distinctness generally falls within the expected range, and most stations have above-average values compared with other monitoring stations around the UK. The W-statistics for Abundance/Biomass Comparison (ABC) plots are usually strongly positive and never negative. There was a sequential change in community composition from the outer to inner stations, which was strongly related to salinity, and, to a lesser extent, sediment granulometry. None of the species regarded as indicators of organic pollution were prominent in the macrobenthic community of Milford Haven Waterway. On this basis, although there are some slight indications of environmental perturbation at particular sites in certain years, it can be concluded that the benthic communities of Milford Haven Waterway are in a healthy state. This study provides a baseline against which the potential effects of any future environmental accidents and/or the increased industrial development can be assessed.

Oceans doi: 10.3390/oceans6010001

Authors: Jon Henderson Georgia Holly Arturo Rey da Silva Athena Trakadas

This paper considers the importance of including Marine Cultural Heritage (MCH) in the UN Decade of Ocean Science for Sustainable Development (2021–2030) in order to fully address the challenges facing the health of our oceans. It outlines the aims and objectives of the Cultural Heritage Framework Programme (CHFP), an official action of the UN Decade of Ocean Science and the only one that specifically deals with cultural heritage. The role of MCH in the Decade is discussed, and its under-appreciation in the UNESCO Cultural Conventions is outlined. The paper then presents the activities of the CHFP, discussing the main themes identified to date, and finishes by outlining the initiative’s next steps.

Oceans doi: 10.3390/oceans5040056

Authors: Joyce Dias Gois Rodrigues de Queiroz Débora Gutierrez Helena Maria Gregório Pina Calado

The ocean is increasingly affected by the rise in maritime activities. Increased anthropogenic pressures have led to environmental impacts and also intensified competition for space and resources among various socioeconomic sectors. To mitigate these impacts on marine ecosystems and reduce conflicts, management tools and processes such as marine protected areas (MPAs) and maritime spatial planning (MSP) have become more prevalent. Trade-offs are inherent to these, and necessary to meet specific conservation and socioeconomic goals. In response, understanding and managing these trade-offs has become crucial to achieving ocean sustainability. This study performs a bibliometric review to identify the types of trade-offs discussed in the marine literature and examines their operationalization for the conservation and sustainable use of marine resources. The analysis reveals that trade-offs, particularly those between conservation and development, and the interests of specific stakeholders, are most frequently addressed in the trade-off literature and are typically approached through integrative methods. This comprehensive examination highlights the significance of recognizing and addressing trade-offs to achieve effective marine management and conservation, aligning ecological integrity with socioeconomic interests.

Oceans doi: 10.3390/oceans5040055

Authors: Lars Kumala Hans Ulrik Riisgård

Filter-feeding sponges capture suspended food particles from ambient water, but little is known about the response of sponges to high food concentrations causing superfluous feeding. Here, through several experimental assays, we studied the relationship between algal concentration in the water column, filtration rate, respiration rate, and specific growth rate in single-osculum Halichondria panicea demosponge explants. Laboratory experiments showed that sponge explants filter the ambient seawater at a maximum rate when exposed to naturally (low) algal concentrations, whereas high algal concentrations resulted in superfluous feeding and reduced filtration rates. Explants maintained at algal concentrations above the incipient overloading concentration level showed that growth rates were in fair agreement with the maximum possible weight-specific growth rate of about 4% d−1. Although the filtration rate became reduced due to overloading, the oxygen extraction efficiency increased, and therefore superfluous feeding did not cause reduced growth. This suggests that H. panicea and probably other sponges have adapted to low algal concentrations, displaying continuous maximum filtration rates. Osculum closure reflects a protection mechanism rather than a physiological regulatory response to high algal concentrations.

Oceans doi: 10.3390/oceans5040054

Authors: Inma Herrera Lidia Yebra Ángelo Santana-del-Pino Santiago Hernández-León

Gaining robust in situ estimates of the growth rate of marine fish larvae is essential for understanding processes controlling year-class success and developing sustainable management strategies to maintain good environmental status. We measured the growth rate of Atlantic herring (Clupea harengus) larvae in the laboratory and compared it to the activity of aminoacyl-tRNA synthetases (AARS). Larvae were reared under controlled conditions for 20 days at three temperatures (7, 12, and 17 °C) using different prey concentrations (0.1, 0.3, and 2 prey·mL−1) of the copepod Acartia tonsa. The relationship between specific growth rates (SGR) and specific AARS activities was best described by a linear function—SGR = −0.1031 + 0.0017 · spAARS, r2 = 0.71, p < 0.05—when only larvae fed ad libitum were considered regardless of the temperature. When larvae fed with low concentrations of food were included in the analysis, the relationship was SGR = −0.0332 + 0.0010 · spAARS, r2 = 0.42, p < 0.05. This latter slope was rather low compared to other studies performed in zooplankton. We suggest protein degradation during the early life stages of fish as the cause of this low slope. We also studied SGR under food deprivation and the effect on specific AARS activities. We found rather high specific AARS activities in small individuals of early stages of fish, also suggesting protein degradation. Further research about protein degradation and turnover rates is needed in order to use AARS activity as a proxy for growth rates in field-caught larvae.

Oceans doi: 10.3390/oceans5040053

Authors: Elena Bisinicu Luminita Lazar

Mesozooplankton are highly responsive to environmental changes, making their population dynamics and species composition important indicators of large-scale oceanic conditions. This study investigates the mesozooplankton composition, emphasizing biomass values across all three marine reporting units in the Romanian Black Sea from 2013 to 2020, covering 45 stations that represent transitional, coastal, and marine waters during the warm season. It also examines environmental parameters, such as temperature, salinity, and nutrient levels associated with eutrophication, that impact the mesozooplankton, as well as the environmental status of the pelagic habitat in this region, influenced by various hydrological and anthropogenic factors. Statistical analyses, including multivariate methods, were employed to investigate correlations between mesozooplankton biomass and environmental parameters, facilitating ecological assessments in accordance with the Marine Strategy Framework Directive (MSFD) Descriptors 1 (Biodiversity) and 5 (Eutrophication) using indicators such as Mesozooplankton bBiomass, Copepoda Biomass, and Noctiluca scintillans iomass. The results indicated that Mesozooplankton and Copepoda Biomass did not reach good ecological status (GES). However, the Noctiluca scintillans Biomass indicator demonstrated that all marine reporting units achieved GES during the warm seasons. These findings underscore the dynamic nature of pelagic habitats and highlight the importance of ongoing monitoring to inform policy and conservation efforts.

Oceans doi: 10.3390/oceans5040052

Authors: Francisco J. Rodríguez-Dopico A. Álvarez García Javier Tarrío-Saavedra

The shipping industry faces the challenge of expanding its capabilities and mitigating its environmental impact. The utilization of adhesive bonding techniques has the potential to facilitate the construction of lighter ships with a reduced carbon footprint. In this work, a complete methodology has been established to study the properties of an adhesive bond between naval steel and the behavior of the bulk adhesive when introduced into seawater. Thermogravimetric analysis (TGA) has been used to determine the thermal properties. Single-lap-joint and tensile tests have been performed showing the negative influence of temperature on the mechanical properties. Seawater absorption has been studied by gravimetric tests. Differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and mechanical bulk tests have been carried out before and after aging. The water absorption is Fickian, and when a constant load is applied, the absorption occurs faster and in greater quantity, decreasing the stiffness and strength. An increase in the glass transition temperature was observed in the absence of a load, with no discernible change upon the application of load condition. Also, aged specimens with constant load exhibited a reduction in water content. These phenomena may be attributed to several diffusion processes.

Oceans doi: 10.3390/oceans5040051

Authors: Shadan Nasseri Doust Mehrnoosh Abbasian S. Abbas Haghshenas Michael J. Risk Craig A. Downs

The decline of natural coral reefs has spurred interest in artificial reef construction and reef rehabilitation efforts. However, many restoration programs are failing because of poor water quality and localized pollution factors. This paper examines one etiology of coral restoration failure, highlighting the need for careful site selection based on hydrodynamic, biological, and pollution criteria. Using Kish Island as a case study, we outline a procedure for determining placement of artificial reefs to minimize external pollution impacts, which could be applied to any reef site worldwide. Our integration of computational modeling and geographic information systems enables the tracking of pollution dispersion and increases the power of restoration efforts. The RQ Plume modeling, used alongside compound pollutant modeling, can identify hotspots with the highest potential to degrade marine environments, particularly reefs. Conservation efforts should prioritize pollution mitigation, as seen in the case of sunscreen pollutants at Kish Island, where regulatory action and public education can contribute to reef protection. This comprehensive approach underscores the critical role of water quality in successful reef restoration and conservation strategies.

Oceans doi: 10.3390/oceans5040050

Authors: Lowri O’Neill Bettina Walter Richard K. F. Unsworth

There is increasing interest in the role that seagrasses play in storing carbon in the context of climate mitigation, but many knowledge gaps in the factors controlling this storage exist. Here, we provide a small case study that examines the role of infaunal biodiversity in influencing seagrass and the carbon stored in its sediments. A total of 25 species of invertebrate were recorded in an intertidal Zostera marina meadow, where these species were dominated by polychaete worms with no bivalves present. We find organic carbon storage (within the top 20 cm) measured by AFDW to be highly variable within a small area of seagrass meadow ranging from 2961 gC.m−2 to 11,620 gC.m−2 with an average (±sd) of 64602 ± 3274 gC.m−2. Our analysis indicates that infaunal communities are significantly and negatively correlated with this sediment organic carbon. However, this effect is not as influential as hypothesised, and the relatively small sample size of the present study limits its ability to provide strong causality. Other factors, such as algal abundance, curiously had a potentially stronger influence on the carbon in the upper sediments. The increasing richness of infauna is likely reducing the build-up of organic carbon, reducing its ecosystem service role. We believe this to likely be the result of bioturbation by specific species such as Arenicola marina and Ampharete acutifrons. A change in sediment organic carbon suggests that these species could be key drivers of bioturbator-initiated redox-driven organic matter turnovers, influencing the microbial processes and remobilizing sediment compounds. Bioturbators should be considered as a limitation to Corg storage when managing seagrass Corg stocks; however, bioturbation is a natural process that can be moderated when an ecosystem is less influenced by anthropogenic change. The present study only provides small-scale correlative evidence with a range of surprising results; confirming these results within temperate seagrasses requires examining this process at large spatial scales or with _targeted experiments.

Oceans doi: 10.3390/oceans5040049

Authors: Sandra Copeto Sara Ganço Inês João Ferreira Didier Sanchez Maria João Nunes Carla Motta Marco Silva Mário Diniz

Perfluorooctanoic acid (PFOA) has been widely studied due to its environmental persistence and bioaccumulation potential, raising concerns about its effects on aquatic life. This research evaluates the impact of PFOA on the antioxidant defenses and stress response systems of the mussel Mytilus galloprovincialis. Mussels were exposed to three concentrations of PFOA (1, 10, and 100 µg·L−1) over 28 days. Several biomarkers, including glutathione S-transferase (GST), superoxide dismutase (SOD), catalase (CAT), lipid peroxidation (LPO), total antioxidant capacity (TAC), vitellogenin (VTG), ubiquitin (UBI), and caspase-3 (CASP) were analyzed. The results suggest stress responses, particularly in animals exposed to higher concentrations, as shown by GST and SOD activities which increased according to PFOA concentrations. Additionally, oxidative stress markers such as MDA and CAT showed variable responses depending on the exposure concentration tested. This study underscores the need for further investigation into the effects of PFOA on mollusks but also the need to unveil gender-specific responses in aquatic organisms exposed to this contaminant. The concentrations of PFOA used in our research are lower than those examined in previous studies, providing crucial insights into the impacts of even minimal exposure levels. It highlights the potential of M. galloprovincialis as a bioindicator in environmental monitoring programs, providing crucial insights for environmental management and policymaking regarding regulating and monitoring PFOA in marine settings. Consequently, in a country where seafood consumption is the second largest in Europe, implementing environmental policies and regulatory measures to manage and monitor PFOA levels in marine environments is crucial.

Oceans doi: 10.3390/oceans5040048

Authors: Abdulhaleem H. Labban H. M. Hasanean Ali Almahri Ali Salem Al-Sakkaf Mahmoud A. A. Hussein

The current study looks at how the characteristics of Arabian Sea tropical cyclones (TCs) change over time. The results show that in the pre-monsoon (April–June) and the post-monsoon (October–December), the activity of TCs > 34 knots, including cyclonic storm (CS), severe cyclonic storm (SCS), very severe cyclonic storm (VSCS), extreme severe cyclonic storm (ESCS), and super cyclonic storm (Sup. CS), has significantly increased, while the tendency of TCs < 34 knots, depressions and deep depressions (Ds) over the Arabian Sea has only slightly increased. Most of the TC activity in the first two decades (1982–2001) over the Arabian Sea activated on the eastern side, while in the last two decades (2002–2021), there was an expansion toward the southwest region of the Arabian Sea, especially in the post-monsoon season. The composite analysis of environmental parameters over the Arabian Sea reveals that the negative anomalies of outgoing longwave radiation (OLR) and the positive anomalies of relative humidity at 500 hPa (RH–500 hPa) in the first decade (1982–1991) and the second decade (1992–2001) are more concentrated on the eastern side of the Arabian Sea, leading to increased activity for TCs. Decades three (2002–2011) and four (2012–2021) demonstrated a wide distribution of weak vertical wind shear (VWS) and strong convection (OLR and RH–500 hPa) over the Arabian Sea basin. This led to TCs occurring more frequently and stronger, especially in the post-monsoon season. SST over the Arabian Sea was sufficient for tropical storm activity (≥26.5 °C) for both typical seasons.

Oceans doi: 10.3390/oceans5040047

Authors: Ezra Roesch Jack H. Rosencrans Kent A. Hatch Robert W. Thacker

Invasive marine invertebrates are increasingly recognized as a potential disturbance to coastal ecosystems. We sought to better document the taxonomic composition of subtidal communities around Long Island to obtain a baseline that can be used to monitor current and future invasions of non-indigenous species. We placed settlement blocks at 18 sites along the coast of Long Island, New York, for three months. After recovering blocks at 12 sites, we analyzed the taxonomic composition of fouling communities on the blocks. We observed 64 invertebrate and 3 algal taxa, with large variation in taxon richness among sites. Multivariate analyses revealed that although taxon composition was significantly dissimilar between north and south shores, variation in dissimilarity did not differ significantly between shores. The high variability in taxon composition observed among sites indicates that additional research is needed to expand our knowledge of invertebrate diversity in the waters surrounding Long Island. Adding more sites and replicate blocks within sites could improve future sampling designs. This research will benefit continuing efforts to monitor, manage, and prevent the establishment of marine invasive species.

Oceans doi: 10.3390/oceans5040046

Authors: Marco Simões Sónia Cotrim Marques Cátia Costa Maria da Luz Calado Jorge Lobo-Arteaga Cátia Bartilotti Maria Jorge Campos Sérgio Miguel Leandro Agostinho Antunes

Understanding the ecological dynamics of zooplankton communities is crucial to precisely assessing the health of marine ecosystems and their management. Metabarcoding has contributed to a better understanding of biodiversity in marine environments. However, this methodology still requires protocol optimisation. Here, we used a complementary approach combining molecular and morphological identification methods to identify the zooplankton community inhabiting the Berlengas Archipelago, Portugal. The presence of non-indigenous species was also assessed. The results showed that the metabarcoding approach outperformed the classical morphological identification method, detecting more species with higher resolution. Nevertheless, the classical method was able to identify species that were not detected by the molecular approaches, probably due to a lack of reference data in the databases. The comparison between different molecular approaches showed that COI and bulk DNA gave better results than 18S rRNA and eDNA by detecting higher species diversity. However, complementarities were observed between them. Molecular tools also proved effective in identifying several potential non-indigenous species, identifying, for the first time, several potentially unreported NIS inhabiting the Portuguese marine ecosystems. Overall, our results confirmed the importance of combining both classical and molecular methods to obtain a more refined assessment of the zooplanktonic communities in marine environments.

Oceans doi: 10.3390/oceans5040045

Authors: Josep L. Pelegrí Mariona Claret Pablo Sangrà

In Cartesian coordinates x,y,z, the gradient Richardson number Ri is the ratio between the square of the buoyancy frequency N and the square of the vertical shear S, Ri=N2/S2, where N2=−g/ρ ∂ρ/∂z and S2=∂u/∂z2+∂v/∂z2, with ρ potential density, u,v the horizontal velocity components and g gravity acceleration. In isopycnic coordinates x,y,ρ, Ri is expressed as the ratio between M2≡N−2 and the squared diapycnal shear Sρ2=ρ/g2∂u/∂ρ2+∂v/∂ρ2, Ri=M2/Sρ2. This could suggest that a decrease (increase) in stratification brings a decrease (increase) in dynamic stability in Cartesian coordinates, but a stability increase (decrease) in isopycnic coordinates. The apparently different role of stratification arises because S and Sρ are related through the stratification itself, Sρ=S/N2. In terms of characteristic times, this is equivalent to τ≡Sρ=to2/td, which is interpreted as a critical dynamic time τ that equals the buoyancy period to≡N−1 normalized by the ratio td/to, where td=S−1 is the deformation time. Here we follow simple arguments and use field data from three different regions (island shelf break, Gulf Stream and Mediterranean outflow) to endorse the usefulness of the isopycnal approach. In particular, we define the reduced squared diapycnal shear σρ2=Sρ2−M2 and compare it with the reduced squared vertical σ2=S2−N2, both being positive (negative) for unstable (stable) conditions. While both Ri and σ2 remain highly variable for all stratification conditions, the mean σρ2 values approach Sρ2 with increasing stratification. Further, the field data follow the relation σρ2=1−Ri/N2Ri, with a subcritical Ri=0.22 for both the island shelf break and the Mediterranean outflow. We propose σρ2 and Sρ2 to be good indexes for the occurrence of effective mixing under highly stratified conditions.

Oceans doi: 10.3390/oceans5040044

Authors: Ana A. Silva Joana Castro André Cid Sérgio M. Jesus Fábio L. Matos

Recent years have seen a notable rise in dolphin-watching boat activities along the Algarve coast in Portugal, potentially affecting the common dolphin (Delphinus delphis) and bottlenose dolphin (Tursiops truncatus) local populations. This study examines the impact of increasing underwater noise levels from these boats on dolphin vocalizations. Field recordings were conducted from June to September 2022, analyzing dolphin whistles in various boat presence scenarios. The results indicate significant changes in whistle-frequency characteristics with boat presence, including increased start, low, and high frequencies, alongside a decrease in the number of inflection points in modulated whistles. The changes might negatively impact dolphin populations viability, underscoring the need for further research. Additionally, improved mitigation strategies may be necessary to reduce the potential negative effects of dolphin watching on cetacean communication and behavior in the Algarve region.

Oceans doi: 10.3390/oceans5040043

Authors: Tamar Shemesh Shani Levy Abigail Einbinder Itai Kolsky Jessica Bellworthy Tali Mass

Global climate change is profoundly impacting coral ecosystems. Rising sea surface temperatures, in particular, disrupt coral reproductive synchrony, cause bleaching, and mortality. Oculina patagonica, a temperate scleractinian coral abundant across the Mediterranean Sea, can grow at a temperature range of 10–31 °C. Studies conducted three decades ago documented this species bleaching during the summer months, the same time as its gonads mature. However, the Eastern Mediterranean Sea is experiencing some of the fastest-warming sea surface temperatures worldwide. This study repeated the year-round in situ assessment of the reproductive cycle and gonad development and correlation to summer bleaching. In addition, thermal performance of the holobiont was assessed in an ex situ thermal stress experiment. In situ monitoring revealed no temporal changes in gonad development compared to previous studies, despite sea surface warming and concurrent bleaching. Experimental thermal performance curves indicated that photosynthetic rate peaked at 23 °C, bleached coral area was significant at 29 °C, and peaked at 34 °C. With local sea surface temperature reaching 31 °C, O. patagonica is exposed beyond its bleaching threshold during the summer months in situ. Despite this, O. patagonica maintains gonad development and physiologically recovers at the end of summer demonstrating resilience to current warming trends.

Oceans doi: 10.3390/oceans5040042

Authors: Smiljko Rudan Šimun Sviličić

Wind-induced waves can lead to the partial or complete wash-over of beaches, causing erosion that impacts both the landscape and tourist infrastructure. In some regions of the world, e.g., Croatia, this process, which usually occurs during a harsh winter, has a major impact on the environment and the economy, and preventing or reducing this process is highly desirable. One of the simplest methods to reduce or prevent beach erosion is the use of innovative underwater structures designed to decrease wave energy by reducing wave height. In this study, submerged breakwaters are numerically investigated using various topologies, positions, and angles relative to the free surface. Not only is the optimal topology determined, but the most efficient arrangement of multiple breakwaters is also determined. The advantage of newly developed submerged breakwaters over traditional ones (rock-fixed piers) is that they do not require complex construction, massive foundations, or high investment costs. Instead, they comprise simple floating bodies connected to the seabed by mooring lines. This design makes them not only cheap, adaptable, and easy to install but also environmentally friendly, as they have little impact on the seabed and the environment. To evaluate wave damping effectiveness, the incompressible computational fluid dynamics (ICFD) method is used, which enables the use of a turbulence model and the possibility of accurate wave modelling.

Oceans doi: 10.3390/oceans5030041

Authors: Salvatore Rosario Bassolillo Egidio D’Amato Salvatore Iacono Silvia Pennino Antonio Scamardella

This research focuses on integrating seakeeping indices into the trajectory planning of a mother ship in order to minimize risks during UAV (unmanned aerial vehicle) takeoff and landing in challenging sea conditions. By considering vessel dynamics and environmental factors, the proposed trajectory planning algorithm computes optimal paths that prioritize the stability and safety of the ship, mitigating the impact of adverse weather on UAV operations. Specifically, the new adaptive weather routing model presented is based on a genetic algorithm. The model uses the previously evaluated response amplitude operators (RAOs) for the reference ship at different velocities and encounter angles, along with weather forecast data provided by the global wave model (GWAM). Preliminary evaluations confirm the effectiveness of the presented model in significantly improving the reliability of autonomous UAV operations from a mother ship across all encountered sea state conditions, particularly when compared with a graph-based solution. The current results clearly demonstrate that it is possible to achieve appreciable improvements in ship seakeeping performance, thereby making UAV-related operations safer.

Oceans doi: 10.3390/oceans5030040

Authors: Andrea Lombardo Giuliana Marletta

The Magnisi peninsula is a small portion of land located near the largest Italian petrol-chemical pole of Augusta–Priolo–Melilli (40 km2), which, since the 1950s, devastated the local environment and landscape and unloaded directly into the sea an impressive quantity of pollutants. Unlike the terrestrial part of the area, where a Natural Oriented Reserve (NOR) called “Saline di Priolo” was established in the 2000s, no concrete legislative action has been implemented or proposed for the marine environment. At the same time, the fauna of the marine environment has not been studied in the same way as that of the terrestrial environment. As concerns the molluscan fauna, most of the information dates back to the 1800s. These studies were exclusively focused on the shells of some mollusks in the area. Instead, no study related to this area has ever been carried out on the group of sea slugs. This study conducted between 2022 and 2023, through snorkeling activities, allowed to provide the first faunistic list of the sea slugs of this area, together with information on the biology and ecology of these gastropods, highlighting the potential biodiversity present in this small stretch of coastline affected by high industrial pollution.

Oceans doi: 10.3390/oceans5030039

Authors: Mark Dingli Kristian Guillaumier Adam Gauci

The accumulation of sea-surface debris around the coastal waters of Malta poses significant ecological and environmental challenges, negatively affecting marine ecosystems and human activities. This issue is exacerbated due to the lack of an effective system tailored to predict surface-debris movement specifically for the Islands of Malta. To address this gap, a pipeline that combines a machine learning-based prediction system with a physics-based model is proposed. This pipeline uses data on historical sea-surface current velocities to forecast future conditions and visualise debris movement. Central to this system are two machine learning models trained to predict surface velocities for the next 24 h for a specific area. These predictions are then utilised in a Lagrangian model to simulate and visualise the debris movement, providing insights into future dispersion patterns. A comparative evaluation of both models using real-world data is made to determine which one performs best in this application. This method offers a tailored approach to addressing sea-surface debris around Malta by accurately predicting sea-surface current velocities and visualising debris movement, improving cleanup operations and marine conservation strategies.

Oceans doi: 10.3390/oceans5030038

Authors: Helder P. B. Nunes Cristiana Maduro-Dias Joana Carvalho Alfredo Borba

The expansion of the invasive Asian macroalgae Rugulopteryx okamurae along the coasts of the Azores represents a significant challenge for local marine biodiversity. A promising approach to managing the biomass produced by this alien alga is to valorize it in the context of the blue economy. This study characterizes and evaluates the potential of R. okamurae biomass for incorporation into cattle feed, with a focus on mitigating enteric methane production. The nutritional value of R. okamurae, its digestibility, and its potential as a mitigating agent for enteric methane production were analyzed in vitro. The results indicate that the inclusion of 5% R. okamurae in the diet significantly (p < 0.05) reduced accumulated methane production by 98% after 24 h of incubation. The addition of 1% algae over the same period resulted in a 38% reduction in methane production. However, a significant decrease (p < 0.05) in gas production of 57.02% and 73.5% was also observed in relation to control, with the inclusion of 1% and 5%, respectively, during 96 h. Nutritionally, R. okamurae was found to have a crude protein content of 18.68% and fiber (NDF) of 55.71% of DM. It is also worth highlighting the high content of ash (31.86%) that was identified in these brown macroalgae. In conclusion, the fresh biomass of R. okamurae could serve as a functional ingredient in cattle feed to mitigate enteric methane production, provided it is used in low percentages. However, it is important to emphasize that high concentrations in the first 12 h did not produce methane, which is also not recommended for enteric fermentation. However, before including it in animal feed, in vivo tests are needed to assess its toxicity.

Oceans doi: 10.3390/oceans5030037

Authors: Elizabeth Durán-Campos David Alberto Salas-de-León Erik Coria-Monter María Adela Monreal-Gómez Benjamín Quiroz-Martínez

This paper assessed the phytoplankton structure and its relationship with the physical environment in the coastal region off Mazatlán, Mexico, in two seasons of 2022, a year in which a strong La Niña event took place: (1) the warmer (August) and (2) the transitional period to the cold phase (November), based on hydrographic data and samples collected in two systematic scientific expeditions. The results showed clear differences between both seasons. Regarding total abundance, August reached 125,200 cells L−1, while November amounted to 219,900 cells L−1. Regarding species composition, the diatoms Cylindrotheca closterium and Planktoniella sol were dominant in August, while Thalassionema nitzschioides and Tetramphora decussata dominated the assemblages in November. The dinoflagellate Protoperidinium punctulatum was dominant in both seasons. However, very marked differences in its abundance are reported. The differences observed in the species richness and abundance could be attributed to the physical configuration of the water column, particularly the surface temperature, which showed clear changes between both seasons. The results presented here confirmed the high phytoplankton richness (some of them with the potential to generate harmful algal blooms), abundance, and diversity values of the region, suggesting a strong relationship with the physical environment.

Oceans doi: 10.3390/oceans5030036

Authors: José J. Hernández Ayala Rafael Méndez-Tejeda

This study investigates the temporal trends and correlations between Saharan dust mass concentration densities (DMCD) and Sargassum concentrations (SCT) in the tropical North Atlantic. Average DMCD data for June, July, and August from 1980 to 2022, alongside SCT data for the same months from 2012 to 2022, were analyzed using Mann–Kendall tests for trends and lagged regression models to assess whether higher Saharan dust levels correlate with Sargassum outbreaks in the region. A comprehensive analysis reveals a significant upward trend in Saharan dust quantities over the study period, with the summer months of June, July, and August exhibiting consistent increases. Notably, 2018 and 2020 recorded the highest mean DMCD levels, with June showing the most significant increasing trend, peaking in 2019. These findings are consistent with previous studies indicating a continuous elevation in Saharan dust concentrations in the tropical atmosphere of the North Atlantic. Simultaneously, Sargassum concentrations also show a notable increasing trend, particularly in 2018, which experienced both peak SCT and elevated DMCD levels. Mann–Kendall tests confirm statistically significant upward trends in both Saharan dust and Sargassum concentrations. Simple linear regression and lagged regression analyses reveal positive correlations between DMCD and SCT, highlighting a temporal component with stronger associations observed in July and the overall June–July–August (JJA) period. These results underscore the potential contribution of elevated Saharan dust concentrations to the recent surge in Sargassum outbreaks in the tropical North Atlantic. Furthermore, the results from forward stepwise regression (FSR) models indicate that DMCD and chlorophyll (CHLO) are the most critical predictors of SCT for the summer months, while sea surface temperature (SST) was not a significant predictor. These findings emphasize the importance of monitoring Saharan dust and chlorophyll trends in the Eastern Caribbean, as both factors are essential for improving Sargassum modeling and prediction in the region. This study provides valuable insights into the climatic factors influencing marine ecosystems and highlights the need for integrated environmental monitoring to manage the impacts on coastal economies.

Oceans doi: 10.3390/oceans5030035

Authors: Manos Potiris Ioannis G. Mamoutos Elina Tragou Vassilis Zervakis Dimitris Kassis Dionysios Ballas

The formation of dense water in the Aegean Sea is important as it affects the deep circulation and the hydrography of the Eastern Mediterranean Sea. In this study, the variability of dense water formation is investigated in relation to forcing mechanisms from 1947 to 2023 in the subbasins of the Aegean Sea, utilising in situ observations from various sources, which have been analysed in combination with satellite altimetry and reanalyses products. The analysis reveals that the Aegean Sea has been in a state of increased dense water formation since 2017 due to the combination of increased surface buoyancy loss and reduced Black Sea water inflow. Extremely high salinity has been recorded in the intermediate layers of the Aegean Sea since 2019. The anticyclonic circulation of the North Ionian gyre during 2017 and 2018 probably also contributed to the rapid transport of highly saline waters in the intermediate and, through dense water formation, the deep layers of the Aegean Sea in 2019. Until 2022, the dense waters formed during the peak of the Eastern Mediterranean Transient still occupied the bottom layers of some deep subbasins of the North and South Aegean; however, the 29.4 kg m−3 isopycnal in the North Aegean and the 29.3 kg m−3 isopycnal in the Southeastern Aegean have gradually deepened by 800 m, permitting the waters forming in the last ten years in the Aegean Sea to settle at ever greater depths. Temperature controls the density variability of the Cretan intermediate water up to the decadal time scale. Increased data availability since 2010 was sufficient to clarify that intrusions of dense water from the North–Central Aegean Sea contributed to the erosion of the Eastern Mediterranean transitional waters in the South Aegean Sea after 2017, as well as to raising the intermediate water masses of the South Aegean to shallower depths. The erosion of the transitional Mediterranean waters in the South Aegean Sea between 1947 and 1955 and 1973 and 1980 coincided with increased dense water formation in the North–Central Aegean Sea. During the peak of the Eastern Mediterranean Transient, the North Ionian circulation, the Black Sea water inflow, the Atlantic Multidecadal Oscillation, and the surface buoyancy fluxes favoured dense water formation in the Aegean Sea.

Oceans doi: 10.3390/oceans5030034

Authors: Luca Russo Carola Murano Domenico D’Alelio

The forty-year-old Long-Term Ecological Research MareChiara (LTER-MC) program started on 26 January 1984, with fortnightly oceanographic sampling until 1991 and then, from 1995, with weekly sampling up to the present time. LTER-MC produced >150 publications that have been cited by thousands of other studies. In this scoping review, we analyzed this corpus using a semantic approach based on topic modeling, a machine-driven procedure to identify and map topics and their interactions. Understanding the causes behind the evolution of scientific topics, their emergence, splitting, hybridization, or merging within a scientific community is an important step in science policy in managing collaborative research and bringing it into the future. Across different topics, mainly represented by studies on Natural History, Biodiversity, Phenology, Life Cycles, and Community Ecology, the LTER-MC work expanded the knowledge on planktonic organisms, describing in detail their lifestyles and delineating their relationships with environmental conditions. In presenting these results, the potential strengths, weaknesses, opportunities, and threats connected to the overall scientific dimension of LTER-MC are discussed. Finally, the upcoming effort is envisioned in reinforcing internal collaboration to integrate basic and applied research around scientific investigations suitable for establishing a stronger interaction between science and policy, as indicated by the United Nations Decade of Ocean Science for Sustainable Development.

Oceans doi: 10.3390/oceans5030033

Authors: Marta Dias Pedro Pousão-Ferreira Mário S. Diniz António Marques Rui Rosa Patrícia Anacleto Ana L. Maulvault

The impacts of climate change-related stressors are becoming more noticeable in the ocean, particularly in coastal marine ecosystems. Yet limited information still exists on the physiological state and ecological resilience of marine fish species, especially during their early life stages (i.e., larvae and juveniles). The present study investigated the effects of chronic exposure to seawater warming (OW; ΔT = +4 °C) and acidification (OA; ΔpH = −0.3 pH units, equivalent to pCO2~1000 µatm), acting alone or combined (OWA), on juvenile zebra seabream (Diplodus cervinus) physiological resilience, considering distinct levels of biological organization (i.e., biochemical, cell, organ and individual levels). After 60 days of exposure, both stressors, in isolation or combination, significantly decreased specific growth rate (−11% in OW, −42% in OA and −49% in OWA) and leukocyte counts (from −29% in OA and OWA up to −37% in OW) in relation to the control treatment. In addition, a decreased Fulton’s condition index (K) was observed under warming and acidification in combination (−35% in OWA). At the cell level, OW, OA and OWA triggered different biomarker responses in D. cervinus (i.e., up-regulation, down-regulation, or absence of significant effect). In general, the results are suggestive of an antagonistic effect when warming and acidification are combined. OWA yielded the highest integrated biomarker response (IBR) index value in the whole organism, muscle, brain and gills of D. cervinus juveniles, therefore suggesting that the effects of these stressors are more severe when they act together. The distinct patterns observed in each stress scenario highlight the importance of carrying out further studies adjusted to the specificities of different regions, i.e., accounting not only for the type and degree of severity of environmental stressors already felt and/or projected for that specific area, but also the physiological plasticity of species that inhabit a particular ecosystem. The gathered knowledge will allow one to determine the vulnerability of particular marine species and geographic areas and, most importantly, to draw up effective and tailor-made conservation strategies to overcome climate change impacts.

Oceans doi: 10.3390/oceans5030032

Authors: Suvi-Tuuli Lappalainen Ulla Tapaninen Jonne Kotta

Shipping is a vital component of global trade. However, shipping activities have negative environmental impacts, including emissions to air and water. The Baltic Sea is severely affected by eutrophication, mainly due to nutrient inputs, especially nitrogen and phosphorus. Understanding the contributions of various nutrient sources is essential for informed environmental regulation. The aim of this research is to quantify the nutrient content of black and grey water discharged from cargo ships in the Baltic Sea in order to assess their contribution to the total nutrient load. Specifically, this research examines the nitrogen and phosphorus loadings from ships calling the port of HaminaKotka and addresses key questions regarding nutrient generation, discharge proportions, emission shares by ship type, and their importance compared to other sources. Using a methodology based on ship data and nutrient production estimates, this study found that 2545 cargo ships generated a total of 781 kg of nitrogen and 134 kg of phosphorus in their effluents during their voyages to the port in 2021. However, only a small fraction (0.5%) of the cargo ships discharged their wastewater at port reception facilities. This study concludes that nutrient discharges from cargo ships’ wastewaters are relatively small, contributing less than 0.06% phosphorus and 0.01% nitrogen to the total load in the area. This result indicates that the impact of cargo ships’ wastewater on the eutrophication of the Baltic Sea is smaller than previously thought. The methodology used in this study can be applied in other ports and regions to assess nutrient discharges from cargo ships’ wastewaters on a wider scale. Further research is recommended to assess the effectiveness of on-board treatment systems, the impact of other contaminants in wastewater, and the development of port reception facilities to facilitate proper wastewater management in the maritime trade.

Oceans doi: 10.3390/oceans5030031

Authors: Gregory P. Asner Nicholas R. Vaughn Joseph Heckler

Submarine groundwater discharge (SGD) is a recognized contributor to the hydrological and biogeochemical functioning of coral reef ecosystems located along coastlines. However, the distribution, size, and thermal properties of SGD remain poorly understood at most land–reef margins. We developed, deployed, and demonstrated an operational method for airborne detection and mapping of SGD using the 200 km coastline of western Hawai‘i Island as a testing and analysis environment. Airborne high spatial resolution (1 m) thermal imaging produced relative sea surface temperature (SST) maps that aligned geospatially with boat-based transects of SGD presence–absence. Boat-based SST anomaly measurements were highly correlated with airborne SST anomaly measurements (R2 = 0.85; RMSE = 0.04 °C). Resulting maps of the relative difference in SST inside and outside of SGD plumes, called delta-SST, revealed 749 SGD plumes in 200 km of coastline, with nearly half of the SGD plumes smaller than 0.1 ha in size. Only 9% of SGD plumes were ≥1 ha in size, and just 1% were larger than 10 ha. Our findings indicate that small SGD is omnipresent in the nearshore environment. Furthermore, we found that the infrequent, large SGD plumes (>10 ha) displayed the weakest delta-SST values, suggesting that large discharge plumes are not likely to provide cooling refugia to warming coral reefs. Our operational approach can be applied frequently over time to generate SGD information relative to terrestrial substrate, topography, and pollutants. This operational approach will yield new insights into the role that land-to-reef interactions have on the composition and condition of coral reefs along coastlines.

Oceans doi: 10.3390/oceans5030030

Authors: Anestis Gourgiotis Dionisia Koutsi Vasiliki Krommyda Anastasia Stratigea

European strategic policy directions toward a sustainable blue economy have strengthened interest in maritime investments, thus increasing sectoral competition for marine space. Emerging repercussions out of such a rising interest need to be handled by marine spatial planning (MSP) as a means of properly allocating marine space to diverse uses; managing conflicts and promoting synergies among them; and pursuing a multi-use perspective of this space. A critical stage of each MSP exercise is the exploration of land- and marine-based policy directions and their current or potential repercussions in the marine environment. Such an exploration is carried out in this work by means of a qualitative policy review for informing the MSP process in the Northern Aegean Sea, Greece. By delving into diverse policy frameworks at various spatial levels—i.e., local (urban), regional, and national/European—constraints, but also perspectives in policy choices/maritime uses in the MSP context, are identified, thus guiding more informed MSP choices in the specific study region while attaining a successful integration or coordination between land and marine developments.

Oceans doi: 10.3390/oceans5030029

Authors: Anny C. Forero-Mejia Laurent Duchatelet Carina Östman

Cnidome morphology appears to be a valuable tool for anthozoan (Octocarallia, Ceriantharia, and Hexacorallia) taxonomy. Ceriantharian cnidomes consist of b-mastigophores, isorhizas, spirocysts, and ptychocysts, including different subtypes. The b-mastigophores are the most valuable ceriantharian cnidae for species identification. The Ceriantharian b-mastigophore terminology is congruent to the b-mastigophores of Carlgren, b-rhabdoids, including the “faltstück” of Schmidt, spirulae, and also potentially the penicilli of den Hartog. The apical tightly folded, inverted b-mastigophore shafts, the “faltstück”, are important species-specific characteristics due to their various patterns. The mesenterial structures known as craspedonemes, cnidorages, and acontioids also have high taxonomic value. Drop-shaped b-mastigophores might be characteristic nematocysts for mesenteries. The occurrence of isorhizas and striations on the inner ptychocyst capsule walls are other species’ characteristics. The morphological similarities of spirulae and penicilli to b-mastigophores within Hexacorallia are highlighted by naming spirulae and penicilli as b-mastigophores/spirulae and b-mastigophores/penicilli subtypes, respectively. The slight morphological distinction between spirulae and penicilli will doubtfully justify the suborders Spirularia and Penicillaria. The spirocysts presence in Ceriantharia and Hexacorallia indicates a closer relationship between Ceriantharia and Hexacorallia than between Ceriantharia and Octocorallia. Octocorallia are the only anthozoans without spirocysts. This work underlines the importance of cnidome morphological analysis for taxonomic identification and classification.

Oceans doi: 10.3390/oceans5030028

Authors: Michael P. Lesser Marc Slattery Keir J. Macartney

Kahng [...]

Oceans doi: 10.3390/oceans5030027

Authors: Samuel E. Kahng

In warm oligotrophic waters, photosymbiotic coral can flourish across a wide depth range (0–170+ m), extending to depths where light attenuates to ~0.1% of surface values. Conventional wisdom has long assumed that mixotrophic corals must increasingly rely on heterotrophy as the ambient light available to drive photosynthesis decreases with depth. However, evidence challenging this traditional dogma has been accumulating in recent years. Although some evidence suggests that some depth-generalist coral species likely increase their reliance on heterotrophy with increasing depth, there is growing evidence that other species do not. Analysis of bulk stable isotopes (δ13C and δ15N) applied to photosymbiotic corals has been used in several ways to infer their trophic ecology and their relative dependence on symbiont photosynthesis versus heterotrophic feeding. However, metrics based on bulk tissue δ13C and δ15N values are subject to considerable uncertainty due to the multiple factors that can affect their values independent of trophic ecology. These competing factors can be quite challenging to disentangle and have led to inconsistent results and conclusions regarding trends in coral heterotrophy with depth. The evidence to date suggests no uniform trophic pattern with increasing depth or decreasing light. Different corals appear to function differently, which is not surprising given their phylogenetic diversity.

Oceans doi: 10.3390/oceans5030026

Authors: Gorana Jelić Mrčelić Svjetlana Krstulović Šifner Vedrana Nerlović

Macroalgae are beneficial for consumers and producers due to their high productivity, their chemical composition and their efficient cultivation without additional feed. Asia dominates global macroalgae production, while European production is still marginal and mainly based on wild harvesting in the North Atlantic. The European Commission has launched initiatives to promote the sustainable production, safe consumption and innovative use of macroalgae products in European regional seas, including the Mediterranean Sea. A variety of coastal and seabed types and a wide range of environmental conditions make the Mediterranean a hotspot of marine biodiversity while providing good conditions for the cultivation of macroalgae. The aim of this paper is to compare the global macroalgae production and macroalgae production in the Mediterranean Sea, focussing on the cultivation of edible macroalgae. The paper also discusses the limitations and possibilities of macroalgae production in the region. Macroalgae production is one of the most promising sectors of the blue economy in the Mediterranean. The production of edible macroalgae suitable for human consumption has great potential, considering future population growth and related food security and health issues, as well as the additional ecosystem benefits of macroalgae production.

Oceans doi: 10.3390/oceans5030025

Authors: Dimitar Popov Galina Meshkova

Cetacean strandings are valuable sources of data about their life history, health status, population trends, and impact of threats. We examined the strandings along the Bulgarian coast of the Black Sea for a period of 13 years from 2010 to 2022. A total of 1528 cetacean strandings of all three species inhabiting the basin were recorded: 1031 harbour porpoises Phocoena phocoena, 199 bottlenose dolphins Tursiops truncatus, 97 common dolphins Delphinus delphis, 19 delphinids and 182 unidentified. The highest numbers were observed in 2016 and 2022. Monthly peaks for harbour porpoise and bottlenose dolphin were in July and August and for common dolphin in May. An unusually high mortality of porpoise neonates was recorded in 2015 and 2016. The overall sex ratio showed a slightly higher share of males at 120:100. This bias was the most pronounced for males of common dolphins. Spatial distribution varied interspecifically but was predominantly along the southern coast. Bycatch signs were detected in 80 animals including during the turbot fishing ban period, suggesting the existence of illegal fishing operations. All of this highlights the need for better reinforcement and control to ensure both the conservation of endangered cetaceans and the sustainability of fisheries. Improvement in data collection is needed to improve the quality of information.

Oceans doi: 10.3390/oceans5030024

Authors: Judith Mutuku Maria Yanotti Mark Tocock Darla Hatton MacDonald

Microplastics are ubiquitous in marine environments and have been documented across all ocean compartments, especially surface waters, across the world. Even though several studies identify the presence of microplastics in the world’s five oceans, there remains an overt problem of large inconsistencies in their sampling, extraction, and consequent quantification. Despite the complexity of these methodologies, researchers have tried to explore microplastic abundance in ocean surface waters. Using a systematic review approach, a dataset was derived from 73 primary studies undertaken since the year 2010 following the Oslo and Paris Conventions (OSPAR) guidelines to monitor and harmonise marine debris. The results showed differences in the abundance and distribution of microplastics in surface waters across oceans. The overall concentration of microplastics in all five oceans ranged between 0.002 and 62.50 items/m3, with a mean abundance of 2.76 items/m3. The highest mean concentration of microplastics was found in the Atlantic (4.98 items/m3), while the least was observed in the Southern Ocean (0.04 items/m3). While challenging, this paper recommends harmonisation of the sampling, separation, and identification methods across the globe to aid in the design of the appropriate mitigation strategies for reducing marine plastic pollution.

Oceans doi: 10.3390/oceans5020023

Authors: Gian Luca Eusebi Borzelli Ernesto Napolitano Adriana Carillo Maria Vittoria Struglia Massimiliano Palma Roberto Iacono

The Ionian Sea is a crucial intersection for various water masses in the Mediterranean. Its hydrography and dynamics play a significant role in the seawater budgets and biogeochemistry of the neighboring sub-basins. Multiple theories have been formulated to gain a better understanding of the Ionian dynamics. These theories primarily attribute the variability of the near-surface Ionian circulation to internal processes. Here, we utilize horizontal currents and temperature–salinity profiles from the Copernicus reanalysis to examine the contribution of baroclinic modes to the variability of the basin horizontal circulation. Our findings demonstrate that, although the basin vertical structure is characterized by three layers, the primary patterns of the Ionian circulation can be attributed to the first baroclinic mode. This mode, along with the barotropic mode, accounts for over 85% of the overall variability in the Ionian circulation, suggesting that only one of the three interfaces separating the different water masses in the basin is dynamically active. We estimate the depth of this interface to be about 490 m. Additionally, our analysis shows that more than 90% of the kinetic energy over the water column is localized above this interface, indicating that the deep layer of the Ionian is dynamically nearly inert.

Oceans doi: 10.3390/oceans5020022

Authors: Ciera J. Edison Cindy R. Elliser Katrina H. White

Little is known about the in-water behavior and site fidelity of harbor seals (Phoca vitulina richardii), as most photo-identification (photo-ID) studies are typically conducted while they are hauled-out on land. We investigated in-water site fidelity rates and seasonal presence in Burrows Pass, Washington, using photographs collected during a long-term photo-ID and behavioral study from January 2015 through November 2019. There was a minimum of 161 individuals and a maximum of 286 individual harbor seals using Burrows Pass. Harbor seals were present in all seasons, with the lowest sighting rates during summer. Individuals were more likely to be sighted/re-sighted in fall and spring. There was large variations in the level and seasonality of site fidelity among individuals. The majority of seals (69.62%) were seen only once, but 22.69% showed low to moderate site fidelity (2–5 sightings) and 7.69% showed strong site fidelity (≥6 sightings) over seasons and across years. These seasonal variations were likely due to foraging, life history, and individual behavioral variabilities. Studies like this provide necessary information about harbor seal in-water site fidelity and behavior, which are less well known but vitally important in harbor seal management and conservation.

Oceans doi: 10.3390/oceans5020021

Authors: Caitlin E. Tems Eric Tappa

This study presents a high-resolution record of δ15Nsed, which serves as a proxy for water column denitrification and oxygen minimum zone (OMZ) intensity, from the Soledad Basin in the Eastern Tropical North Pacific OMZ. The Soledad Basin δ15Nsed record is compared to the Pescadero Slope and Santa Barbara Basin (SBB) δ15Nsed records to gain insight into regional variations in the ETNP OMZ. During the Medieval Climate Anomaly (MCA; 950–1250 CE), Soledad Basin, Pescadero Slope, and SBB records exhibit coherent trends suggesting that there was general water column oxygenation stability. During the Little Ice Age (LIA; 1350–1850 CE), Soledad Basin and SBB showed a similar decreasing trend in δ15Nsed values while the Pescadero Slope δ15Nsed exhibited an increasing trend until values abruptly declined between 1740 and 1840 CE. We suggest that increased δ15Nsed variability and the different trends at the Pescadero Slope during the LIA are due to the influence of the North American monsoon (NAM), which can suppress upwelling when enhanced and result in OMZ contraction. The decoupling between the Soledad Basin, SBB, and the Pescadero Slope could also be due to the increased influence of enriched 15NO3− subarctic waters in the California Current System. Since each site is influenced by local productivity, basin morphology, and regional atmospheric and ocean circulation patterns, we suggest that assessing OMZ fluctuations from multiple sites provides a more comprehensive view of regional OMZ dynamics in response to climate variations.

Oceans doi: 10.3390/oceans5020020

Authors: Rainer Feistel Olaf Hellmuth

At an energy flux imbalance of about 1 W m−2, the ocean stores 90% of the heat accumulating by global warming. However, neither the causes of this nor the responsible geophysical processes are sufficiently well understood. More detailed investigations of the different phenomena contributing to the oceanic energy balance are warranted. Here, the role of low-level marine clouds in the air–sea interaction is analysed. TEOS-10, the International Thermodynamic Equation of State of Seawater—2010, is exploited for a rigorous thermodynamic description of the climatic trends in the lifted condensation level (LCL) of the marine troposphere. Rising sea surface temperature (SST) at a constant relative humidity (RH) is elevating marine clouds, cooling the cloud base, and reducing downward thermal radiation. This LCL feedback effect is negative and counteracts ocean warming. At the current global mean SST of about 292 K, the net radiative heat flux from the ocean surface to the LCL cloud base is estimated to be 24 W m−2. Per degree of SST increase, this net flux is expected to be enhanced by almost 0.5 W m−2. The climatic LCL feedback effect is relevant for the ocean’s energy balance and may be rigorously thermodynamically modelled in terms of TEOS-10 equations. LCL height may serve as a remotely measured, sensitive estimate for the sea surface’s relative fugacity, or conventional relative humidity.

Oceans doi: 10.3390/oceans5020019

Authors: Elvira Armenio Andrea Tateo Francesca Fedele Nicola Ungaro Michele Mossa Vittorio Esposito Vincenzo Campanaro

A coupled numerical approach that combines the WRF model and the Mike 3 (DHI) hydrodynamic model was developed and applied in two semi-enclosed basins in the Ionian Sea (Italy) to assess the wind-driven current. To gain a better understanding of how the sea current field can vary depending on meteorological data forcing, three different scenario were set up. The sensitivity of the sea current pattern was investigated as a function of the type of meteorological forcing and appreciating the differences in the results. The aims of this study are threefold. Firstly, we wish to define an ad hoc procedure to join the model-computed meteorological parameters in the hydrodynamic model. Secondly, we will investigate the feedback from the Mar Piccolo and Mar Grande basins in the Ionian Sea using fully coupled simulations and an uncoupled system where the atmospheric parameters are derived from a ground station. Finally, we will evaluate the results achieved by applying two scenarios of typical meteorological conditions to the study site. The model results highlighted the variability of sea currents depending on meteorological forcing.

Oceans doi: 10.3390/oceans5020018

Authors: Ashani Arulananthan Venura Herath Sivashanthini Kuganathan Anura Upasanta Akila Harishchandra

We appreciate the comments made by Hendawitharana et al [...]

Oceans doi: 10.3390/oceans5020017

Authors: Manuja Promodya Hendawitharana Adriaan Gittenberger Prabath Krishantha Jayasinghe Deishini Rupika Herath

We are responding to an article by Arulananthan et al [...]

Oceans doi: 10.3390/oceans5020016

Authors: Carlos Saavedra David Cordero

The grooved carpet-shell clam is one of the most economically relevant shellfish species living in the Mediterranean and nearby Atlantic coasts. Previous studies using different types of genetic markers showed a remarkable genetic divergence of the eastern Mediterranean, western Mediterranean, and Atlantic populations, but important details remained unclear. Here, data from six nuclear introns scored for restriction fragment size polymorphisms in eight populations that have not been studied before have been pooled for the analysis with data scattered through three previous studies, totaling 32 samples from 29 locations. The results show lower levels of heterozygosity, higher mean number of alleles, and alleles with restricted distribution in the Mediterranean populations, suggesting the existence of a large, isolated population in the eastern Mediterranean at the middle Pleistocene. The data also confirm the similarity of populations from Tunisia to Western Mediterranean populations. Finally, a genetic mosaic is apparent in the Atlantic coasts of the Iberian Peninsula, with a divergence of Rias Baixas populations from more northern populations and Central Portugal populations. The effects of oceanic fronts, seasonal upwellings, river plumes, and/or fishery management operations could explain this and other features of the Atlantic populations.

Oceans doi: 10.3390/oceans5020015

Authors: Laura García-Salines Pablo Sanchez-Jerez

Artificial coastal structures, such as seawalls, breakwaters, and groins, can exert various impacts on the fish communities in the nearby regions. This study focuses on assessing the ecological effects of coastal infrastructure on marine environments, by comparing, at different seasons, the habitat complexity and heterogeneity, as well as their effects on fish assemblages, between the artificial habitat created with the intention of constructing a marina (Puerto Amor) and the natural habitats surrounding the Cabo de la Huerta area in Alicante (Spain). Employing an asymmetric design and examining two temporal and spatial scales, we utilized visual censuses in snorkeling to gauge the abundance and size of fish species, alongside various parameters related to habitat complexity and heterogeneity. The overarching hypothesis is that fish populations associated with artificial habitats will differ in terms of abundance, biomass, species richness, and diversity compared to fish populations associated with natural habitats, due to changes in complexity and heterogeneity. The findings indicate a shift in fish assemblages; for example, the family Labridae showed differences between the two habitat types for several species. These changes were due to the influences of the Posidonia oceanica meadow and algae like Jania rubens; being influenced by biological variables such as Ellisolandia elongata, Oculina patagonica, and Sarcotragus spinosulus; as well as physical variables such as stones, gravel, and blocks. While there is evidence of alteration in fish assemblages due to changes in habitat structure, there is also an increase in richness (9 species/m2) and total abundance and biomass (1000 ind./m2 and 1700 g/m2, respectively) in the artificial habitat. Multivariate analyses reveal that the fish community in Puerto Amor is less homogeneous than the one in the natural habitat. However, these analyses also indicate an overlap between the communities of both habitats, suggesting substantial similarity despite the noted differences. Consequently, although the habitat alteration has impacted fish populations, it has not diminished abundance, biomass, or species richness. In conclusion, the artificial rocky habitat resulting from the construction attempt at Puerto Amor harbor has fish populations with ecological significance and its removal could lead to undesirable impacts in the area, as the fish assemblages have become well established.

Oceans doi: 10.3390/oceans5020014

Authors: Chen Luo Luofeng Huang

Deformable wave energy converters have significant potential for application as flexible material that can mitigate structural issues, while how to design the dimensions and choose an optimal deployment location remain unclear. In this paper, fully coupled computational fluid dynamics and computational solid mechanics were used to simulate the dynamic interactions between ocean waves and a deformable wave energy converter. The simulation results showed that the relative length to wave, deployment depth and aspect ratio of the device have significant effects on the energy conversion efficiency. By calculating the energy captured per unit width of the device, the energy efficiency was found to be up to 138%. The optimal energy conversion efficiencies were achieved when the structure length was 0.25, 0.5 or 0.75 of the dominating wavelength and submerged at a corresponding suitable depth. The aspect ratio and maximum stress inside the wave energy converter showed a nonlinear trend, with potential optimal points revealed. The simulation approach and results support the future design and optimisation of flexiable wave energy converters or other marine structures with notable deformations.

Oceans doi: 10.3390/oceans5020013

Authors: Ana G. Bonelli Paulina Martin Phillip Noel Gregory P. Asner

Despite the limited coverage of coral reefs in the world’s oceans, they play a crucial role in global marine biodiversity and providing essential ecosystem services. This study explores the influence of chlorophyll-a (Chl-a) concentration in the water column on the estimation of bottom reflectance (rb) in coral reefs monitored by the Allen Coral Atlas coral reef monitoring system, using satellite imagery from a Sentinel-2 MSI sensor. We conducted a comprehensive analysis, considering Chl-a global distribution and variability, and its combined effect with water column depth over rb calculation. Our results demonstrated that the impact of Chl-a on rb estimation becomes significant when the water column depth exceeds 3 m. While suggesting the optionality of using regional Chl-a values, our study highlights potential overestimations of Chl-a in optically complex environments, such as along the Brazilian coast. This research contributes to refining coral reef monitoring systems and underscores the importance of accurate Chl-a assessments for robust environmental evaluations.

Oceans doi: 10.3390/oceans5020012

Authors: Andrés López-Pérez Rebeca Granja-Fernández Eduardo Ramírez-Chávez Omar Valencia-Méndez Fabián A. Rodríguez-Zaragoza Tania González-Mendoza Armando Martínez-Castro

In May 2023, oceanic and atmospheric anomalies indicated El Niño conditions in the eastern Pacific, followed by coral bleaching in coral communities and reefs of Huatulco. We conducted surveys and sampled coral reef communities from late June to mid–August of 2023 to evaluate the intensity and extent of the changes associated with the warming event. From January of 2023, Huatulco experienced positive sea surface temperature (SST) anomalies; however, beginning in June, the high-temperature anomalies became extreme (>31 °C; ~2 °C above historical records). These high temperatures resulted in extensive coral bleaching in middle–late June and mortality from middle–late July (>50–93%). In addition, the area experienced significant reductions in echinoderm abundance and fish biomass. In 2023, severe bleaching affected coral systems in the Central Mexican Pacific, Gulf of Mexico, and Mexican Caribbean, making this the most devastating marine heatwave event, simultaneously impacting coral reefs across Mexico’s Pacific and Atlantic coasts.

Oceans doi: 10.3390/oceans5020011

Authors: Sandra Copeto Sara Ganço Inês João Ferreira Marco Silva Carla Motta Mário Diniz

Tetrabromobisphenol A (TBBPA) is a fire-retardant containing bromine, produced in large quantities worldwide and extensively used in several industrial products. This compound was identified as a potential contaminant of the environment, causing toxicity to organisms. However, its toxicity remains poorly understood in marine bivalves. The first objective of this work was to evaluate the impact of TBBPA on mussels (Mytilus galloprovincialis) exposed for 28 days to various concentrations of TBBPA (0, 1, 10, and 100 µg·L−1), by assessing stress biomarkers’ responses (Glutathione S-transferase, superoxide dismutase, catalase, lipid peroxidation, total antioxidant capacity, total ubiquitin, caspase-3 and acetylcholinesterase). The results showed that lower concentrations (1 and 10 µg·L−1) were efficiently detoxified, as suggested by GST activities, which were supported by the responses of the other biomarkers. The most pronounced effects were observed in animals exposed to the highest concentration of TBBPA (100 µg·L−1), suggesting oxidative stress. Additionally, significant strong correlations were found between total antioxidant capacity and some biomarkers (superoxide dismutase and lipid peroxidation), showing that processes involved in oxidative stress fighting are working to avoid cell injury. In brief, mussels’ defense mechanisms were capable of dealing with exposure to the lower concentrations tested. Despite this, the risk of consuming shellfish or other fishery products contaminated with TBBPA should be a cause for concern.

Oceans doi: 10.3390/oceans5020010

Authors: Vigge Ulfsson Hyeyoung Kim Linnea Cervin Anna Roos Aleksija Neimanis

Harbour porpoises (Phocoena phocoena) are the only cetacean residents found year-round in Swedish waters and they are exposed to numerous natural and anthropogenic threats. Since the in situ monitoring of cetaceans can be difficult, invasive and often expensive, investigation of stranding patterns and examination of stranded animals can be used as a cost-effective source of data to study these elusive animals. The aim of this study was to investigate the spatiotemporal patterns of harbour porpoise stranding reports and the possible underlying causes in Swedish waters over a ten-year period (2014–2023). Additionally, the Swedish stranding network plays a key role in the collection of stranded carcasses for health and disease surveillance, and geographic coverage of the network also was analysed. When making spatial comparisons, the ten-year period was divided into two five-year blocks. Data on 854 stranded harbour porpoises were analysed from the coasts of the Skagerrak, Kattegat, and Baltic Seas. Both significant spatial and temporal patterns could be identified. Strandings peaked in July through September and hotspots occurred along most of the Swedish west coast, with the most frequent hotspots located around Öresund and especially the area around the Kullen peninsula. The spatial patterns of strandings found in this study are consistent with data on porpoise abundance, prey abundance, and gillnet fisheries’ efforts. The latter is known to be one of the primary causes of porpoise mortality. Furthermore, the coverage of the Swedish stranding network increased between the two periods, likely reflecting an increased awareness of the carcass-based surveillance program, and gaps requiring network expansion efforts were identified. These results also provide baseline data to enable the continued monitoring of stranding trends, as changes may indicate changes in population distribution, size or mortality rates.

Oceans doi: 10.3390/oceans5020009

Authors: Tung-Yung Fan Yan-Leng Huang Anderson Mayfield

Since reef-building corals rely on both heterotrophy and endosymbiotic dinoflagellate autotrophy to meet their metabolic needs, it is necessary to consider both food supply and light levels, respectively, when optimizing their cultivation ex situ. Herein nubbins of the model reef coral Pocillopora acuta cultured in recirculating aquaculture systems at photosynthetically active radiation levels of 370 or 670 μmol quanta m−2 s−1 were fed Artemia nauplii at concentrations of either 33 or 78 individuals mL−1 in a separate feeding tank for 6 hr in the dark thrice weekly. A subset of nubbins was experimentally wounded at the outset of the 84-day experiment to assess recovery, and 100% fully healed within 2–4 weeks. All cultured corals survived, and unwounded corals (1) grew at a specific growth rate approaching 0.5% day−1 and (2) demonstrated a mean total linear extension of 0.2% day−1 (~6–8 cm year−1); these are far higher than growth rates normally documented in situ. In the feeding tank, corals tolerated nitrate levels up to 25 mg L−1, but once concentrations reached 50 mg L−1 by day 84, tissue necrosis began to occur in nubbins of one tank. This highlights the importance of feeding in separate tanks during long-term culture of corals, and bio-filtration could reduce the possibility of organic matter accumulation in future coral culture studies.

Oceans doi: 10.3390/oceans5010008

Authors: Fernando P. Santos Teresa L. Rosa Miguel A. Hinostroza Roberto Vettor A. Miguel Piecho-Santos C. Guedes Soares

A prototype of an autonomous system for the retrieval of oceanographic, wave, and meteorologic data was installed and tested in May 2021 on a Portuguese research vessel navigating on the Atlantic Ocean. The system was designed to be installed in fishing vessels that could operate as a distributed network of ocean data collection. It consists of an automatic weather station, a ferrybox with a water pumping system, an inertial measurement unit, a GNSS unit, an onboard desktop computer, and a wave estimator algorithm for wave spectra estimation. Among several parameters collected by this system’s sensors are the air temperature, barometric pressure, humidity, wind speed and direction, sea water temperature, pH, dissolved oxygen, salinity, chlorophyll-a, roll, pitch, heave, true heading, and geolocation of the ship. This paper’s objectives are the following: (1) describe the autonomous prototype; and (2) present the data obtained during a full-scale trial; (3) discuss the results, advantages, and limitations of the system and future developments. Meteorologic measurements were validated by a second weather station onboard. The estimated wave parameters and wave spectra showed good agreement with forecasted data from the Copernicus database. The results are promising, and the system can be a cost-effective solution for voluntary observing ships.

Oceans doi: 10.3390/oceans5010007

Authors: Antonio Bode María Louro Elena Rey Angel Lamas

The subtropical North Atlantic is a key region for understanding climate impact in the ocean. Plankton studies in this region have been generally framed in biogeographic provinces or focused on latitudinal gradients. In this study, we demonstrate the benefits of using empirically constructed continuous gradients versus the use of average values for biogeographical provinces to characterize plankton assemblages along a longitudinal transect at 24.5° N using an unprecedented array of stations including hydrographic observations, abundance of phytoplankton and zooplankton, and plankton size spectra in the epipelagic layer (0–200 m). In addition, the variability of zooplankton assemblages was analyzed using detailed taxonomic identification at selected stations. We found significant gradients in most hydrographic and plankton variables. The former, including surface temperature and salinity, the depth of the upper mixing layer, and the depth of the chlorophyll maximum, displayed non-linear gradients with maximum or minimum values near the center of the transect. In contrast, most plankton variables showed linear zonal gradients. Phytoplankton, microzooplankton (<100 µm), and the slope and the intercept of the size spectra increased (and Trichodesmium decreased) to the west. Total mesozooplankton (>200 µm) did not show any significant zonal pattern, but the taxonomic assemblages were characterized by a gradual replacement of large Calanoids by small-bodied Cyclopoid copepods from east to west. The use of continuous gradients provides more detailed information on the zonal structure of subtropical plankton than the classical approach using discrete areas.

Oceans doi: 10.3390/oceans5010006

Authors: Michael Bennett Antaya March Jeremy Raguain Pierre Failler

Blue carbon has been proposed as a nature-based solution for climate change mitigation; however, a limited number of published works and data and knowledge gaps hinder the development of small island developing states’ (SIDS) national blue carbon resources globally. This paper reviews the blue carbon ecosystems of Seychelles as a case study in the context of SIDS, comparing estimations by the Blue Carbon Lab and recent blue carbon (mangrove and seagrass) evaluations submitted to the Seychelles national government. Mangroves (2195 ha, 80% in Aldabra Atoll) and seagrasses (142,065 ha) dominate in Seychelles, with coral reefs having the potential for carbon sequestration (169,000 ha). Seychelles is on track to protecting its blue carbon, but these systems are threatened by rising sea levels, coastal squeeze, erosion, severe storms, and human activities. The importance of carbon inventories, accounting institutions, and continuous monitoring of blue carbon systems is discussed. Blue accounting is necessary for accurate accounting of carbon sequestration and carbon storage, generating carbon credits, and representing impactful reductions in greenhouse gases for NDCs. Challenges and opportunities include policy legislation regarding ownership rights, accreditation and certification for carbon credits, sustainable financing mechanisms like natural asset companies and blue tokens, local engagement for long-term success, and carbon market dynamics following COP27. The restoration and regulation of blue carbon resources for optimal ecosystem services delivery, carbon inventories, and blue carbon policy are recommended development priorities. Blue carbon ecosystems have the potential to contribute to NDCs of SIDS while simultaneously offering sustainable development pathways for local communities through the multiple ecosystem services they provide.

Oceans doi: 10.3390/oceans5010005

Authors: Nadav Shashar Asa Oren Re’em Neri Omer Waizman Natalie Chernihovsky Jenny Tynyakov

Artificial reefs have been suggested as alternative dive sites to mitigate human pressure on natural reefs. Despite the conceptual appeal of artificial reefs, there is a paucity of empirical evidence regarding their effectiveness in achieving this objective. Here, we report that a small artificial reef deployed adjacent to a local coral marine protected area caused a shift in the routes taken by introductory dives and nearly eliminated their visitations to the natural fringing reef within the MPA. This behavioral shift among divers persisted for more than a decade following the AR deployment. These findings underscore the efficacy of well-designed and appropriately located artificial reefs as valuable instruments in the conservation of coral reefs.

Oceans doi: 10.3390/oceans5010004

Authors: Alexander J. Werth Shirel R. Kahane-Rapport Jean Potvin Jeremy A. Goldbogen Matthew S. Savoca

Baleen whales are ecosystem sentinels of microplastic pollution. Research indicates that they likely ingest millions of anthropogenic microparticles per day when feeding. Their immense prey consumption and filter-feeding behavior put them at risk. However, the role of baleen, the oral filtering structure of mysticete whales, in this process has not been adequately addressed. Using actual baleen tissue from four whale species (fin, humpback, minke, and North Atlantic right) in flow tank experiments, we tested the capture rate of plastics of varying size, shape, and polymer type, as well as chemical residues leached by degraded plastics, all of which accumulated in the baleen filter. Expanded polystyrene foam was the most readily captured type of plastic, followed by fragments, fibers, nurdles, and spherical microbeads. Nurdle and microbead pellets were captured most readily by right whale baleen, and fragments were captured by humpback baleen. Although not all differences between polymer types were statistically significant, buoyant polymers were most often trapped by baleen. Plastics were captured by baleen sections from all regions of a full baleen rack, but were more readily captured by baleen from dorsal and posterior regions. Baleen–plastic interactions underlie various risks to whales, including filter clogging and damage, which may impede feeding. We posit that plastics pose a higher risk to some whale species due to a combination of factors, including filter porosity, diet, habitat and geographic distribution, and foraging ecology and behavior. Certain whale species in specific marine regions are of the greatest concern due to plastic abundance. It is not feasible to remove all plastic from the sea; most of what is there will continue to break into ever-smaller pieces. We suggest that higher priorities be accorded to lessening humans’ dependence on plastics, restricting entry points of plastics into the ocean, and developing biodegradable alternatives.

Oceans doi: 10.3390/oceans5010003

Authors: Patrícia Vicente João Almeida Laura Ribeiro Sara Castanho Ana Candeias-Mendes Pedro Pousão-Ferreira Ana Margarida Faria

Coastal habitats are increasingly threatened by multiple anthropogenic-related activities, which include ocean warming and loss of structural habitat complexity. These two pressures have the potential to severely affect the structure and function of marine biodiversity. Early life stages of many fish species recruit to coastal habitats at the end of their pelagic phase, benefiting from access to food, shelter and protection. However, changes in temperature have been shown to influence ecologically relevant behaviours in post-settlement stage fish, and the loss of structural habitat complexity has been related to low recruitment and deleterious behaviours of fish in coastal habitats. Here, we evaluated the individual and interactive effects of prolonged exposure to increasing temperature and changed structural habitat complexity on routine swimming speed and escape response of post-settlement white seabream, Diplodus sargus (Linnaeus, 1758). Fish were reared under different temperatures (control 19 °C; high 22 °C) and structural habitat complexity (low and high) scenarios, in a cross-experimental design, and the routine swimming and escape responses were analyzed after 6 weeks of exposure. Change in temperature did not induce alterations at the behavioural level, but loss of structural habitat complexity increased speed and distance travelled during routine swimming, and responsiveness to a stimulus during the escape response behaviour. The interaction of the two factors did not influence performance. Determining how species are affected by changes in their environment, and the mechanisms that underlie these changes, will be critical to understanding the fish recruitment and populations’ fitness and survival.

Oceans doi: 10.3390/oceans5010002

Authors: Diana Morales-de-Anda Amílcar Leví Cupul-Magaña Consuelo María Aguilar-Betancourt Gaspar González-Sansón Fabián Alejandro Rodríguez-Zaragoza Alma Paola Rodríguez-Troncoso

Herbivorous fish can mediate spatial competition between algae and corals, which is crucial for coral ecosystems. However, in areas with limited coral coverage like the Mexican tropical Pacific (MTP), this dynamic is not fully understood. This study, using a functional trait approach and ordination analysis, explores whether herbivorous reef fish assemblage influences the benthic habitat components or if physicochemical factors define the habitat variability in the MTP’s Cleofas and Marietas insular systems. We analyzed if this relationship persisted across systems and over time, and identified species traits tied to habitat variability. Island comparison analyses between Cleofas and Marietas reveal that both herbivorous reef fish and physicochemical variables shape the habitat. Cleofas had larger mobile herbivorous fish that formed groups related mostly to macroalgae cover. In contrast, temporal analysis of Marietas shows that the habitat is primarily shaped by physicochemical variables with herbivorous fish being mainly small farmer species related to branching corals. Notably, these closely situated insular systems present varied ecosystem mediators, influenced by diverse drivers including fish traits and environmental factors. This study underscores the potential of employing a framework of ecological species traits combined with ordination methods to unravel the distinct site dynamics that contribute to the persistence of coral ecosystems within the MTP.

Oceans doi: 10.3390/oceans5010001

Authors: Mauricio Ulloa Miguel A. Rivero Antonio Fernández

Strandings caused by anthropogenic factors are one of the most worrying threats in relation to the conservation of cetacean species, and in the case of Chile, due to its geography and large extension of the coastline, monitoring and access to these events is difficult, making their study more complex. Chile has a shortage of specialized scientific forensic research facilities for cetaceans; however, for this study, it was able to collect data recorded from official institutions and sporadic scientific biological sampling oriented to investigate the causes of death or stranding. According to the Chilean government official database, we described that the main causes of unusual mortality events (UME) and mass strandings from 2015 and 2016 were acute poisoning by biotoxins and strandings by multiple possible causes, respectively, while individual strandings would have their causes in anthropogenic activities, such as entanglements in fishing and aquaculture gears and collisions with vessels. The predominant species in mass strandings was the sei whale (Balaenoptera borealis). The geographical area of greatest prominence in mass strandings was the Aysén Region in the Central Patagonia of Chile, while the species mostly involved in individual strandings along the south-central, central, and northern coasts of Chile was the small porpoise (Phocoena spinipinnis). The most common gross pathological findings were advance decay of the carcasses and non-specific wounds of different natures.

Oceans doi: 10.3390/oceans4040029

Authors: Nurul Filzati Ali Leela Rajamani

The Irrawaddy dolphin is found in the coastal and estuarine areas of West Penang, Malaysia. Studies were conducted to estimate the site fidelity, residence index, and population size of Irrawaddy dolphins in West Penang. Photo-identification studies were conducted using boat surveys from 2019 to 2021. Thirty-nine marked Irrawaddy dolphins were identified, with thirty-six newly identified individuals and three individuals observed in 2013. Resightings of four individuals indicated that they were found north of Sungai Burung and Sungai Pinang in West Penang. The majority of individuals had low sighting rates, ranging from 2.6 to 7.7%, with three individuals having medium sighting rates, the highest being 15.4%. The residence index was 0.01 for all 36 individuals, and the highest value of 0.36 was recorded for one individual. Using open population models and closed models, the population size was determined to be 64 or and 52, respectively. The results suggest that although there is a population present, it is probably open, as the residence index is low. The population size appeared to be stable from 2013 to 2021. This information will inform conservation managers of the best way forward for the conservation of Irrawaddy dolphins in Penang.

Oceans doi: 10.3390/oceans4040028

Authors: Leslie B. Hart Miranda Dziobak Randall S. Wells Elizabeth Berens McCabe Eric Conger Tita Curtin Maggie Knight John Weinstein

Microplastic ingestion was reported for common bottlenose dolphins (Tursiops truncatus) inhabiting Sarasota Bay, FL, USA, a community that also has prevalent exposure to plasticizers (i.e., phthalates) at concentrations higher than human reference populations. Exposure sources are currently unknown, but plastic-contaminated prey could be a vector. To explore the potential for trophic exposure, prey fish muscle and gastrointestinal tract (GIT) tissues and contents were screened for suspected microplastics, and particle properties (e.g., color, shape, surface texture) were compared with those observed in gastric samples from free-ranging dolphins. Twenty-nine fish across four species (hardhead catfish, Ariopsis felis; pigfish, Orthopristis chrysoptera; pinfish, Lagodon rhomboides; and Gulf toadfish, Opsanus beta) were collected from Sarasota Bay during September 2022. Overall, 97% of fish (n = 28) had suspected microplastics, and GIT abundance was higher than muscle. Fish and dolphin samples contained fibers and films; however, foams were common in dolphin samples and not observed in fish. Suspected tire wear particles (TWPs) were not in dolphin samples, but 23.1% and 32.0% of fish muscle and GIT samples, respectively, contained at least one suspected TWP. While some similarities in particles were shared between dolphins and fish, small sample sizes and incongruent findings for foams and TWPs suggest further investigation is warranted to understand trophic transfer potential.

Oceans doi: 10.3390/oceans4040027

Authors: Michael P. Lesser

Sponges are increasingly recognized as ecologically important on coral reefs as scleractinian corals decline. Most sponge species can be divided into two symbiotic phenotypes which are characterized as high microbial abundance (HMA) or low microbial abundance (LMA) sponges. Sponge species of HMA or LMA symbiotic phenotypes differ not just in their microbiomes, but in other characteristics, including that LMA sponges actively pump at higher rates than HMA sponges based on a standard normalization to size. This dichotomy has recently been questioned because the size range of LMA sponges used to quantify pumping rates during studies on their trophic ecology were exceedingly small, often less than an order of magnitude. Here, both HMA and LMA sponges, across two to three orders of magnitude in sponge volume (mL) or mass (g) were assessed for allometric relationships between sponge size and pumping rates (Q = mL s−1). The scaling analysis of all data sets combined reveals that HMA sponges scale their pumping rates isometrically with size, while LMA sponges scale their pumping rate allometrically. When HMA species are examined separately, however, tropical HMA sponges scaled isometrically, while temperate HMA sponges scaled allometrically. From an ecological perspective, to quantify differences between HMA and LMA sponges for rate functions of interest (e.g., feeding) it is important to remove the effects of size as a covariate, and adjust the Q values of sponges to a standard volume or mass. For multiple species and geographic locations, this analysis shows that LMA sponges always maintain higher Q values. On tropical coral reefs, the differences between HMA and LMA sponges are intrinsic and constrained by strong evolutionary selection resulting in fixed differences in Q, regardless of sponge size.

Oceans doi: 10.3390/oceans4040026

Authors: Ana Guerreiro Pedro Brito

Gadolinium-based contrast agents (GBCA) are complexes, highly stable in vivo, used in magnetic resonance imaging (MRI), administered in patients and then eliminated via the renal system, passing through wastewater treatment plants (WWTP) before being discarded in the receiving medium, without apparent removal. In this study, it was examined whether different exposure periods to several environmental parameters (solar radiation, different salinities, temperatures and pH) will influence the stability of these complexes, namely, the Gd-DOTA. Gd-DOTA solutions were processed in a seaFAST-pico saline matrix pre-concentration and elimination system, and Gd concentrations were determined using ICP-MS. The results showed that the complex remained stable in fresh, brackish and saline water environments, even when exposed to extreme temperatures (40 °C) or slightly acidic to basic conditions (6–10), for an exposure period of 96 h. A small increase in the free Gd concentration was observed after 18 days when exposed to pH < 4, in all tested salinities (0, 18 and 36 PSU), with a degradation increase of up to 29%, after 5 weeks of exposure in freshwater. When exposed to direct solar radiation, a low Gd-DOTA degradation (4%) was observed after 24 h at salinity 18 PSU and remained constant until the end of the exposure period (96 h), while the remaining salinities showed negligible values.

Oceans doi: 10.3390/oceans4040025

Authors: Nitin Agarwala Cherdvong Saengsupavanich

Seaports are gateways that connect a nation to the world economy. With trade by sea increasing due to globalization, the need for the improvement and development of seaports cannot be overlooked. While the development of ports is considered essential for the economic growth and prosperity of a nation, they also result in environmental deterioration that can hurt the future of humanity. The factors that cause such deterioration are many and have been discussed and studied in some detail over the years. Of these, however, studies associated with the environmental impacts of seaports emanating from the oceanfront are limited. It is with this understanding that the current work discusses the physical and biological impacts that occur due to the oceanic environment in seaports, the existing policy provisions, and the possible ways ahead to reduce environmental deterioration and allow their sustainable operation, by means of reviewing published works.

Oceans doi: 10.3390/oceans4040024

Authors: Violeta Martínez-Castillo Alma Paola Rodríguez-Troncoso Amílcar Leví Cupul-Magaña

Intervention techniques to restore coral communities have become an important management tool to help recover and rehabilitate damaged reefs. The direct transplantation of healthy coral fragments is the most common method; however, there is controversy in the long-term success, as using coral clones may diminish the genetic diversity of the coral population. Genetic recombination can be achieved when the coral colony produces gametes and eventually reproduces; therefore, it is important to provide evidence that restored colonies produce gametes as their naturally recruited counterparts with similar colony size (age). Natural and restored Pocillopora coral colonies of the same size range (between 40 and 50 cm in diameter) were tagged and sampled during the rainy season to determine gamete maturation. Our results show no differences in the reproductive activity among colonies: natural and restored coral colonies matured gametes from June to October, with a peak in sexually active coral colonies in July. Also, gamete malformation was not observed. During the gamete production period, the area’s temperature ranged from 27.9 to 30.02 °C. The results’ evidence that coral colonies formed through active restoration contribute not only to the increase in live coral cover as seen in previous studies but potentially contribute in the medium term (>5 years after out-planting) to the production of larvae and local and subsidiary recruitment, since they exhibit the same reproductive patterns as their naturally formed counterparts and no differences in the reproductive activity among coral colonies. Therefore, long-term coral restoration projects contribute to maintaining the live coral cover and the genetic diversity in the region, eventually rehabilitating the coral community.

Oceans doi: 10.3390/oceans4040023

Authors: Abdenaim Minoubi Nezha Mejjad Khalid El Khalidi Mohammed Bouchkara Ahmed Fadili Mohamed Chaibi Bendahhou Zourarah

This study assesses the spatial distribution and contamination level of heavy metals in Safi Bay surface sediments. In this order, 28 surface sediment samples were retrieved from the study area and analyzed using the x-fluorescence method. To assess the contamination of the examined sediment, we used geo-ecological indices such as contamination factor (CF), degree of contamination (DC), geo accumulation index, and pollution load index (PLI). The results show that only Pb and Cd present moderate and considerable contamination in some sampling sites, while other elements (Cr, Cu, Zn, and Ni) indicate no contamination and low contamination by these elements. The inhomogeneous distribution of metal concentrations along the bay suggests different heavy metal sources. Given the ecological and socioeconomic importance of the study area, there is a need for a further analysis of both sediments and biological samples for a better understanding of the contamination levels and origin of metals, in addition to the sustainability of Safi Bay.

Oceans doi: 10.3390/oceans4030022

Authors: Fabio Quezada-Perez Sebastián Mena Cindy Fernández-García Juan José Alvarado

In the past decades, one of the most widely reported phenomena on Caribbean reefs is the general fall in coral cover and rise in macroalgae. Reefs with low coral cover and high macroalgal abundances are often presumed to provide poorer ecosystem functions and services. In this study, we assessed the condition of coral reefs on the Caribbean Coast of Costa Rica and determined how eight key ecosystem metrics varied in response to different coral and fleshy macroalgae covers. Most reefs surveyed had high fleshy macroalgae and low live coral covers, with an average (±SD) of 31 ± 28% and 14 ± 13% per site. The value of many of the ecosystem metrics estimated for coral reefs of the region appears to be lower than what has been reported for other areas in the Caribbean. We found that the rugosity, urchin density, fish richness, total fish biomass, large fish density, and the potential fishery value of the reef were higher in sites with low fleshy macroalgae covers (<10%). Our results concur with the prevailing paradigm that an increase in macroalgae abundance could reduce the ecosystem services provided by coral reefs.

Oceans doi: 10.3390/oceans4030021

Authors: Maria Carla Benedetti Lorenzo Bramanti Giovanni Santangelo

The recruitment process is a fundamental step in population life cycles that determines survival, population demographic structure, and dynamics. The success of recruitment events repeated over successive years greatly affects the survival of long-lived gorgonian populations. Here, we report the recruitment process of the precious, heavily harvested Mediterranean gorgonian Corallium rubrum (red coral) on both settlement tiles and natural substrates over different Mediterranean areas. Red coral is a gonochoric internal brooder that reproduces in early summer. Lecithotrophic planulae settle 15–30 days after release in semi-dark environments at depths between 15 and 800 m. In autumn, 0.58–0.68 mm-wide recruits can be observed on the vaults of small crevices and caves and on rocky cliffs and boulders. Owing to their small size, there is limited knowledge of C. rubrum recruitment in the field. In this study, we examined the recruitment density and distribution in Canadells (Banyuls sur Mer, France) and Calafuria (Livorno, Italy) and compared these findings with those collected over different Mediterranean areas. Red coral exhibited high recruitment values ranging from 0.43 to 13.19 recruits dm−2. The distribution pattern of recruits, examined at a small spatial scale via nearest-neighbor distance analysis, revealed a significantly higher patch frequency on the natural substrate than on settlement tiles, presumably because of the scarcely available spots of free space on the former substrate, which are crowded by competitor species.

Oceans doi: 10.3390/oceans4030020

Authors: Jonathan Teague John C. C. Day Michael J. Allen Thomas B. Scott Eric J. Hochberg David Megson-Smith

The use of hyperspectral imaging in marine applications is limited, largely due to the cost-prohibitive nature of the technology and the risk of submerging such expensive electronics. Here, we examine the use of low-cost (<5000 GBP) hyperspectral imaging as a potential addition to the marine monitoring toolbox. Using coral reefs in Bermuda as a case study and a trial for the technology, data was collected across two reef morphologies, representing fringing reefs and patch reefs. Hyperspectral data of various coral species, Montastraea cavernosa, Diploria labyrinthiformis, Pseudodiploria strigosa, and Plexaurella sp., were successfully captured and analyzed, indicating the practicality and suitability of underwater hyperspectral imaging for use in coral reef assessment. The spectral data was also used to demonstrate simple spectral classification to provide values of the percentage coverage of benthic habitat types. Finally, the raw image data was used to generate digital elevation models to measure the physical structure of corals, providing another data type able to be used in reef assessments. Future improvements were also suggested regarding how to improve the spectral data captured by the technique to account for the accurate application of correction algorithms.

Oceans doi: 10.3390/oceans4030019

Authors: Dave Anderson Laurie Shuster Cindy R. Elliser Katrina MacIver Erin Johns Gless Johannes Krieger Anna Hall

Harbor porpoises are typically seen in small groups of 1–3 individuals, with aggregations of 20+ individuals treated as rare events. Since the 1990s, the harbor porpoise population in the Salish Sea has seen a significant recovery, and an increased number of observed aggregations that exceed the more usual small group sizes has been observed in recent years. By combining the observational data of United States and Canadian research organizations, community scientists, and whale watch captains or naturalists, we demonstrate that harbor porpoise aggregations appear to be more common than previously known, with 160 aggregations documented in 2022 alone. Behavioral data also indicate that foraging behaviors are common and social behaviors, like mating, are seen more often during these encounters compared to small groups. Other behaviors that are considered to be rare or unknown were also observed during these encounters, including cooperative foraging and vessel approach. These aggregations are likely important foraging and social gatherings for harbor porpoises. This holistic approach integrating data from two countries and multiple sources provides a population level assessment that more effectively reflects the behavior of harbor porpoises in this region, which do not recognize the socio-political boundaries imposed upon the natural world.

Oceans doi: 10.3390/oceans4030018

Authors: Yuya Nakamura Haochen Zhang Atsushi Yamaguchi

In the oceans, Chaetognatha can contribute significantly to the total zooplankton biomass (up to 10–30%). The genus Eukrohnia, the dominant Chaetognath genus in the western subarctic Pacific, includes E. hamata and E. bathypelagica. Although it has been pointed out that there is no genetic difference between the two species, no study has been made that treats them as the same species group. In this study, we investigated vertical distribution based on the eight vertical stratification samplings down to 1000 m depths conducted day/night at four seasons covering one year, community structure, and population structure of the three dominant Chaetognath species: Parasagitta elegans, E. hamata, and E. bathypelagica in the western subarctic Pacific. The population densities of each species at 0–1000 m water column were 0.04–0.36 ind. m−3 for P. elegans, 0.14–1.60 ind. m−3 for E. hamata, 0.24–1.54 ind. m−3 for E. bathypelagica, and 1.37–2.62 ind. m−3 for Eukrohnia juveniles. The vertical distributions were consistent both day and night, and no diel changes were observed for all species throughout the seasons. The vertical distribution of Chaetognaths evaluated by the distribution center was 61–169 m for P. elegans, 143–206 m for Eukrohnia juveniles, 134–279 m for E. hamata, and 253–612 m for E. bathypelagica. The body length of P. elegans ranged from 4 to 34 mm, and one to three cohorts were identified at each sampling occasion. While the presence of the eight stages has been reported for Eukrohnia, only one to five stages occurred, and specimens belonging to six to eight stages were not observed in the samples throughout the year. The body length of the whole Eukrohnia species ranged from 2 to 14 mm. The body length histograms of the Eukrohnia species group, including E. hamata and E. bathypelagica, and their juveniles showed the presence of two to four cohorts at each sampling date. Within the Eukrohnia species group, vertical changes in body length were present, which were characterized by the smaller specimens occurring at shallower depths, followed by an increase in body length with increasing depths. From the vertical distribution and population structure of the Eukrohnia species group (Eukrohnia juvenile + E. hamata + E. bathypelagica) in this study, there was no difficulty in treating them as one species. It may suggest that E. hamata and E. bathypelagica in the western subarctic Pacific could be treated as one species group. To clarify this point, a detailed genetic analysis of the Eukrohnia species group will be needed for future studies.

Oceans doi: 10.3390/oceans4030017

Authors: Mari Aizawa Tian Gao Atsushi Yamaguchi

Hydrozoans are numerically dominant taxa in gelatinous zooplankton communities of the worldwide oceans and play an energy transfer role connecting primary producers and higher trophic level organisms. In the western subarctic Pacific, St. K2 has been established as a long-term time-series monitoring station. Various studies on zooplankton have been conducted, while hydrozoans have not been treated. This study presents the abundance, vertical distribution, and population structure of the dominant hydrozoan species (Aglantha digitale) at St. K2. Samples collected by vertical stratification samplings from eight layers of 0–1000 m both day and night during four seasons in one year. Hydrozoans occur throughout the year. The annual mean abundance of A. digitale was 198.4 ind. m−2 and composed of 91.9% of hydrozoans. The vertical distribution of A. digitale was concentrated for the epipelagic layer (0–200 m), both day and night of the most season. The bell height (BH) of A. digitale ranged between 2.4–18.9 mm. Most of the mature individuals, with gonad length larger than 10% of BH, occurred only in July. The BH of mature individuals ranged from 4.7 to 17.6 mm, with the BH of most mature individuals were larger than >10 mm. Through observation on BH at each sampling layer, small individuals with BH < 6 mm were distributed below 300 m depths throughout the seasons, expanding their vertical distribution to the deeper layers. Inter-region comparison of abundance, maturation body size, and generation length of A. digitale revealed that these parameters are varied with the region and depend on the marine ecosystem structures.

Oceans doi: 10.3390/oceans4030016

Authors: Erika Gress Tom C. Bridge Justin Fyfe Gemma Galbraith

Herbivorous fishes play important functional roles in coral reef ecosystems, and their influence on mediating competitive dynamics between corals and macroalgae is well studied. Nonetheless, direct interactions between herbivorous fishes and corals may also be relevant, although these are less studied. Here, we describe a series of observations of schools of the herbivorous streaked rabbitfish (Siganus javus) nibbling on black corals (order Antipatharia) at the SS Yongala wreck, within the Great Barrier Reef Marine Park. We provide a hypothesis that may explain this behaviour, which, if confirmed, would represent a mechanism influencing the health of the corals. Moreover, this interaction extends the typical coral–algae competition for space paradigm and furthers knowledge of complex relationships between coral reef organisms.

Oceans doi: 10.3390/oceans4030015

Authors: Francisco Leitão

The influence of environmental variables (oceanographic and climatic) on the catch rates of striped red mullet (Mullus surmuletus) by artisanal fishery was investigated using different time series models (Dynamic Factorial Analyses; Min-Max Factorial Analyses and Generalized Least Square models). Climatic and oceanographic survey data were collected at different areas of the Portuguese coast (Northwestern, Southwestern and South-Algarve) with distinct oceanographic regimes. Time series analyses reveal an effect of fishing effort in catch rates in Southwestern areas. Variability in M. surmuletus catch rates was associated to regional environmental multi-controls. Upwelling and westerly winds were the main drivers of catch rates variability across the three areas but the type of relationship varied among them. A consistent relationship between catch rates and environment factors was identified during the peak period of seasonal recruitment (spring to summer) in Southwest and South-Algarve coast, with Upwelling-summer and Sea surface temperature-spring affecting short term (lag 2 years) catch rates. In South-Algarve the increase in SST in summer, during peak of spawning, was correlated with the catch rate increase with a lag of two years. Environmental effect on catch rates reveals that fisheries management needs to accommodate the regional effect of environment variables on species biology to better define future assessment plans (catch limits).

Oceans doi: 10.3390/oceans4020014

Authors: Erin D’Agnese Ryan J. McLaughlin Mary-Anne Lea Esteban Soto Woutrina A. Smith John P. Bowman

In Tasmania, Australian fur seals (Arctocephalus pusillus doriferus) regularly interact with Atlantic salmon (Salmo salmar L.) aquaculture lease operations and opportunistically consume fish. The microbial communities of seals and aquaculture salmon were analyzed for potential indicators of microbial sharing and to determine the potential effects of interactions on wild seal microbiome composition. The high-throughput sequencing of the V1–V3 region of the 16S rRNA genes from the gut microbial communities of 221 fur seals was performed: 41 males caught at farms, 50 adult scats from haul-outs near farms, 24 necropsied seals, and controls from Bass Strait breeding colonies, encompassing 56 adult scats and 50 pup swabs. QIIME2 and R Studio were used for analysis. Foraging at or near salmon farms significantly shifted seal microbiome biodiversity. Taxonomic analysis showed a greater divergence in Bacteroidota representatives in male seals captured at farms compared to all other groups. Pathogens were identified that could be monitoring _targets. Potential indicator amplicon sequence variants were found across a variety of taxa and could be used as minimally invasive indicators for interactions at this interface. The diversity and taxonomic shifts in the microbial communities of seals indicate a need to further study this interface for broader ecological implications.

Oceans doi: 10.3390/oceans4020013

Authors: Mohamed F. M. Fairoz Kevin T. Green Kuwaja N. M. Sajith Weerathunga A. S. Chamika Amarasingha M. K. N. Kularathna Saichetana Macherla Douglas S. Naliboff Ana Cobián-Güemes Linda Wegley-Kelly Forest Rohwer

Coral reefs around Sri Lanka have coexisted with human communities for thousands of years and are a continual source of food, economic productivity, and tourism. Although these reef systems sustain nearby populations, little is known about the presence or functional role of microbial communities on reefs dominated by hard corals or fleshy algae. Coral reef benthos cover was recorded, and reef-associated water samples were collected, sequenced and analyzed from seven coral reefs around Sri Lanka. Microbial metagenomes were analyzed to reveal both the taxonomic and metabolic makeup of the microbial communities present at each site. A metagenomic analysis of microbial phyla showed that Alphaproteobacteria and Gammaproteobacteria were most abundant, constituting up to 79.4% of microbial communities. At the order level, Rhodobacterales dominated the microbial communities across all sites, with the exception of the Paraviwella coral reef, where the order Alteromonadales dominated. A Principal Component Analysis (PCA) was performed using metagenomic sequence data to find the possible trends of interactions and drivers of taxonomic and metabolic community structure. This study is the first microbial metagenome dataset of coral reef associated water from the Indian Ocean continental island, Sri Lanka. These data further confirm the need for a comprehensive study of reefs in Sri Lanka aimed at elucidating the processes involved in microbial energy utilization.

Oceans doi: 10.3390/oceans4020012

Authors: Carlos Gómez Andrés Acosta-Chaparro Cesar Bernal Diana Gómez-López Raúl Navas-Camacho David Alonso

Natural processes such as upwelling of deeper-water masses change the physical-chemical conditions of the water column creating localized ocean acidification events that can have an impact on the natural communities. This study was performed in a coral reef system of an archetypical bay within the Tayrona National Natural Park (PNNT) (Colombia), and aimed to quantify net calcification rates of a foundational coral species within a temporal context (6 months) taking into account the dynamics of seasonal upwelling that influence the study area. Net calcification rates of coral fragments were obtained in situ by the alkalinity anomaly technique in short-term incubations (~2.5 h). We found a significant effect of the upwelling on net calcification rates (Gnet) (p < 0.05) with an 42% increase in CaCO3 accretion compared to non-upwelling season. We found an increase in total alkalinity (AT) and dissolved inorganic carbon (DIC) with decreased aragonite saturation (Ωara) for the upwelling months, indicating an influence of the Subtropical Under Water mass (SAW) in the PNNT coral community. Significant negative correlations between net calcification with temperature and Ωara, which indicates a positive response of M. auretenra with the upwelling conditions, thus, acting as “enhancer” of resilience for coral calcification.

Oceans doi: 10.3390/oceans4020011

Authors: Charel Wohl Queralt Güell-Bujons Yaiza M. Castillo Albert Calbet Rafel Simó

A range of volatile organic compounds (VOCs) have been found to be released during zooplankton grazing on microalgae cultivated for commercial purposes. However, production of grazing-derived VOCs from environmentally relevant species and their potential contribution to oceanic emissions to the atmosphere remains largely unexplored. Here, we aimed to qualitatively explore the suite of VOCs produced due to grazing using laboratory cultures of the marine microalga Isochrysis galbana and the herbivorous heterotrophic dinoflagellate Oxyrrhis marina with and without antibiotic treatment. The VOCs were measured using a Vocus proton-transfer-reaction time-of-flight mass spectrometer, coupled to a segmented flow coil equilibrator. We found alternative increases of dimethyl sulfide by up to 0.2 nmol dm−3 and methanethiol by up to 10 pmol dm−3 depending on the presence or absence of bacteria regulated by antibiotic treatment. Additionally, toluene and xylene increased by about 30 pmol dm−3 and 10 pmol dm−3, respectively during grazing only, supporting a biological source for these compounds. Overall, our results highlight that VOCs beyond dimethyl sulfide are released due to grazing, and prompt further quantification of this source in budgets and process-based understanding of VOC cycling in the surface ocean.

Oceans doi: 10.3390/oceans4020010

Authors: Zahidah Afrin Nisa

To achieve coral reef resilience under Agenda 2030, island governments need to institutionalise a competent blue workforce to expand their reef resilience initiatives across economic organisations and industries. The ability of island governments to shape new policies for sustainable island development relying on natural capital, such as coral reefs, has been hampered by structural and institutional deficiencies on both sides of the science-policy interface (SPI) at the UN. Using a qualitative research design, this article explores the science-policy interface (SPI) policy paper, Rebuilding Coral Reefs: A Decadal Grand Challenge and the role of this SPI in guiding UN coral reef financing for island states. This article uses the dive industry to investigate the needs of policymakers in island states via a conceptual framework for policy analysis. This article highlights the gaps of the SPI from the perspective of the global south and is beneficial for the islands selected under the Global Coral Reef Investment Plan. The article highlights the results of the SPI to island decision makers, which indicate that, without a policy framework that includes space for industrial policy within UN SPI, island governments will continue to fall into financial traps that constrain their efforts in operationalising their blue workforce. The study concludes that interlinked SDGs, such as SDG 9 and SDG 8, which focus on linking industrial innovation and infrastructure with decent work, as well as SDG 16 and 14.7, provide SIDS institutions with integrated policy approaches capable of bridging the divides between the scientific community, the diving industry, and island governments and that this needs to be further explored at all levels.

Oceans doi: 10.3390/oceans4010009

Authors: Serena Anselmi Francesca Provenza Tecla Bentivoglio Giuseppe Picerno Andrea Cavallo Monia Renzi

Pollution of the marine environment by microfibers is considered a problem for ecosystem conservation. The amount of microplastic, localization of sources, and associated ecotoxicity are well known in the literature. Wastewater from washing machines is the main source of microplastic fibers in the aquatic environment, and fabrics made from recycled plastic are widely reused. The circular economy also promotes recycling of dyed natural wool materials as a basis for making new clothing, but in this case, less research has been conducted on the behaviour and effects of recycled wool microfibers in marine ecosystems. MWool® (MW) and MWool® carded (MWc) products made from recycled wool fibers were tested in mesocosms to investigate the biodegradation of wool fibers over a 260-day period and the effects of this process on marine ecosystems in terms of microfiber inputs and the ecotoxicological effects of by-products and chemicals released during degradation. The early degradation process was associated with the loss of artificial pigments from the dyed wool, particularly pink and red, which occurred within 30–90 days of exposure. Mean release of microparticles into contact water is significantly different from control (T0, p < 0.01) at 90 days MWc (36.6 mg/L) and 180 days MW (42.9 mg/L). The biodegradation process is accompanied by swelling of wool fibers, which is associated with a significant increase in mean wool thickness (p < 0.05, 18.8 ± 2.1 µm at T0 vs. 24.0 ± 7.1 µm). In both cases, the contact water was not associated with signs of ecotoxicity for the marine species tested in this study (Phaeodactylum tricornutum, Brachionus plicatilis, and Paracentrotus lividus).

Oceans doi: 10.3390/oceans4010008

Authors: Laura Pérez-Sampablo Pedro Osuna Bernardo Esquivel-Trava Nicolas Rascle Francisco J. Ocampo-Torres

The impact of the high space-temporal variability of the wind field during the moderate and intense storm stages of a tropical cyclone on the wave field as computed by the numerical model WaveWatch III is investigated in this work. The realistic wind fields are generated by a high-resolution implementation of the HWRF model in the Gulf of Mexico and stored over 15 min intervals. The spatial structure of the wind field computed by HWRF is highly variable in space and time, although its mean structure is very similar to that described for parametric hurricanes already specified in the previous studies. The resulting storm-generated wave fields have a persistent structure, with wave maxima present in the forward quadrants of the storm and in the rear quadrant II. This structure is determined by the strong winds and the extended fetch condition in quadrants I and II, as well as by the translation speed of the storm. When a shorter time interval is analyzed (e.g., a 3 h period, when the storm becomes a category 1 hurricane), the structure of the mean wind field may differ greatly from the mean field calculated with a sufficiently longer period; however, the spatial distribution of the wave field around the hurricane tends to maintain its typical spatial structure. The use of wind fields with reduced time variability (e.g., with a 3 h moving average) does not change the structure of the mean wave field, but reduces the mean wave height values by up to 10%.

Oceans doi: 10.3390/oceans4010007

Authors: Alice G. Bianchi Christian Wild Monica Montefalcone Enzo Benincasa Yusuf C. El-Khaled

In the Mediterranean, the fleshy, mat-forming red alga Phyllophora crispa creates high-biodiversity habitats that influence light availability, water movement, and temperature. However, knowledge about its influence on other key environmental parameters, such as oxygen availability, chlorophyll, and turbidity, is missing. Therefore, we conducted an in situ study in the Western Mediterranean Sea using multiparameter probes that were placed multiple times on algal P. crispa mats, in adjacent Posidonia oceanica seagrass meadows, and on bare hard bottoms. We acquired a total of 17 full diel measurements for dissolved oxygen (DO), chlorophyll, and turbidity in September and October 2019. Results showed that P. crispa mats influence the investigated parameters differently when compared to P. oceanica meadows and that a monthly effect was observed. In September, general DO patterns measured for P. crispa mats and P. oceanica meadows follow the daily cycle depending on light availability, with the measured DO being lower in the P. oceanica meadows compared to the P. crispa mats and the hard-bottom habitats. In October, however, no significant difference in DO concentrations was observed between P. crispa mats and P. oceanica meadows. Results of this study corroborate that P. crispa mats can be viewed as an ecosystem engineering species, influencing environmental parameters and, hence, providing a habitat for outstanding associated biodiversity.

Oceans doi: 10.3390/oceans4010006

Authors: Erica Terese Krueger Janina V. Büscher David A. Hoey David Taylor Peter J. O’Reilly Quentin G. Crowley

Ocean acidification (OA) has provoked changes in the carbonate saturation state that may alter the formation and structural biomineralisation of calcium carbonate exoskeletons for marine organisms. Biomineral production in organisms such as cold-water corals (CWC) rely on available carbonate in the water column and the ability of the organism to sequester ions from seawater or nutrients for the formation and growth of a skeletal structure. As an important habitat structuring species, it is essential to examine the impact that anthropogenic stressors (i.e., OA and rising seawater temperatures) have on living corals and the structural properties of dead coral skeletons; these are important contributors to the entire reef structure and the stability of CWC mounds. In this study, dead coral skeletons in seawater were exposed to various levels of pCO2 and different temperatures over a 12-month period. Nanoindentation was subsequently conducted to assess the structural properties of coral samples’ elasticity (E) and hardness (H), whereas the amount of dissolution was assessed through scanning electron microscopy. Overall, CWC samples exposed to elevated pCO2 and temperature show changes in properties which leave them more susceptible to breakage and may in turn negatively impact the formation and stability of CWC mound development.

Oceans doi: 10.3390/oceans4010005

Authors: Yen-Huei Li Barbara Calcinai Jiayi Lim Christine H. L. Schönberg

Coral reefs are in decline globally, resulting in changed constructive and destructive processes. The South China Sea is a marginal sea that is of high biological importance, but also subjected to extreme local and global pressures. Yet, the regional calcium carbonate dynamics are not well understood, especially bioerosion. A literature search for research on bioerosion and bioeroders in the South China Sea found only 31 publications on bioerosion-related research and 22 biodiversity checklists that contained bioeroders, thus generating a paltry bibliography. Bioerosion research in the South China Sea is still undeveloped and reached only two publications per year over the last few years. Hong Kong is the hotspot of activities as measured in output and diversity of methods, but the research in Hong Kong and elsewhere was strongly favoring field surveys of sea urchins over other bioeroders. Overall, macroborers received almost equal attention as grazer-eroders, but interest in microborers was low. Almost 90% of the research was conducted by local workers, but 90% of the publications were still disseminated in English. Field surveys and laboratory analyses made up over 40% of the research, but experimental work was mostly missing and represents the largest, most important gap. A government initiative in Thailand generated much knowledge on the distribution of marine sponges; otherwise urchins were again prominent in diversity checklists. Comparatively, many checklists were produced for Vietnam from work by visiting scientists. Most studies investigated coastal habitats, but a fourth sampled at oceanic locations. About 36% of the checklist publications covered the entire South China Sea; the rest produced faunistic records for locations within single countries. Our efforts demonstrate that, while active bioerosion research and basic expertise exist in the South China Sea, research remained unrepresentative with respect to taxa, ecofunctional guilds, and especially to controlled experiments. The latter are urgently needed for prognoses, modelling and management in this populated and overused marine environment.

Oceans doi: 10.3390/oceans4010004

Authors: Oceans Editorial Office Oceans Editorial Office

High-quality academic publishing is built on rigorous peer review [...]

Oceans doi: 10.3390/oceans4010003

Authors: Ángel Mateo-Ramírez Pablo Marina Alejandro Martín-Arjona Elena Bañares-España José E. García Raso José L. Rueda Javier Urra

Meadows of the seagrass Posidonia oceanica inhabit most infralittoral bottoms of the Mediterranean Sea and are considered one of the main climax stages of the infralittoral environment. This seagrass has its western distributional limit along the coast of the Alboran Sea. Taking into account the decline of P. oceanica meadows and the global scenario of ocean warming, it becomes essential to know the structure, temporal dynamics, sexual reproduction and conservation status of this seagrass, across its geographical distribution, including the distribution boundaries where the meadows withstand limiting environmental conditions. In the present work, we studied the structure, phenology and flowering events of four P. oceanica meadows located in the northwestern Alboran Sea (close to the Strait of Gibraltar). Results indicate a decreasing trend of patch size, bathymetric range and number of leaves per shoot towards the Strait (and the Atlantic Ocean), as well as an increasing trend of shoot density and leaf height. Phenological parameters of the northwestern Alboran Sea P. oceanica meadows presented temporal dynamics similar to meadows from other locations within the biogeographical distribution of this seagrass, with similar or even less annual variability in the former. Although most of the studied P. oceanica meadows seem to present a good health status (BiPo index ~0.6) with high shoot densities and some flowering events, some of them showed evidence of regression.

Oceans doi: 10.3390/oceans4010002

Authors: Austin Bowden-Kerby

The widespread demise of coral reefs due to climate change is now a certainty, and investing in restoration without facing this stark reality risks failure. The 50 Reefs Initiative, the dominant adaptation model for coral reefs is examined, and a new coral-focused paradigm is proposed, based on helping coral reefs adapt to rising temperature, to ensure that as many coral species as possible survive locally over time. With pilot sites established in six Pacific Island nations, genebank nurseries of bleaching resistant corals are secured in cooler waters, to help prevent their demise as heat stress increases. Unbleached corals selected during bleaching events are included. From these nurseries corals are harvested to create nucleation patches of genetically diverse pre-adapted corals, which become reproductively, ecologically and biologically viable at reef scale, spreading out over time. This “Reefs of Hope” paradigm, modelled on tropical forest restoration, creates dense coral patches, using larger transplants or multiple small fragments elevated on structures, forming fish habitat immediately. The fish help increase coral and substratum health, which presumably will enhance natural larval-based recovery processes. We also hypothesize that incoming coral recruits, attracted to the patch, are inoculated by heat adapted algal symbionts, facilitating adaptation of the wider reef. With global emissions out of control, the most we can hope for is to buy precious time for coral reefs by saving coral species and coral diversity that will not likely survive unassisted.

Oceans doi: 10.3390/oceans4010001

Authors: Shuichi Fujiwara Daisuke Kezuka Kazutaka Hagiwara Hiroo Ishimori Hideo Tabata

The substratum structure is critical for facilitating settlement and increasing the survivorship of coral settlers. However, knowledge about its structural complexity is largely lacking. In this study, we examined the effect of complexity on the settlement and post-settlement survivorship of coral settlers using four types of structures: groove, using a CSD (Coral Settlement Device, 4.5 cm φ × 2.5 cm H, top-shaped ceramic); flat, using a CP (Ceramic Plate, 29.5 cm L × 3.1 cm W × 0.9 cm H, unglazed ceramic plate); linear, using a CN (Coral Net, mesh size 19 mm, biodegradable plastic net); and wrinkle, using a SS (Scallop Shell, 11.0 cm in shell length). The complexity was obtained from the ratio of the surface area to the vertically projected area of the substratum. The substratum sets were installed in the coral reef around the Ryukyu Islands every May from 2012 to 2014. After about 2 or 6 months of spawning, a certain number of substratum types were sampled, and the number of coral spats that settled on them was counted by taxa classified into Acropora, Pocilloporidae, Millepora, and Others. The larval settlement rate in the first set of samples and the survivorship of coral spats in the second set of samples were estimated. The mean settlement rate was, in order, the CSD; SS; CN; and CP, and the mean survivorship was, in order, the CSD; CP; SS; and CN, over three years. A positive correlation was found between the structural complexity, mean settlement rate, and mean survivorship. Our results show that the structural complexity of coral seedlings affects the settlement of coral larvae and the survivorship of coral spats.

Oceans doi: 10.3390/oceans3040036

Authors: Jonathan Teague Jack Willans David A. Megson-Smith John C. C. Day Michael J. Allen Thomas B. Scott

Rising oceanic temperatures create more frequent coral bleaching events worldwide and as such there exists a need for rapid, non-destructive survey techniques to gather greater and higher definition information than that offered by traditional spectral based monitoring systems. Here, we examine thermally induced laboratory bleaching of Montipora capricornis and Montipora confusa samples, utilising hyperspectral data to gain an understanding of coral bleaching from a spectral standpoint. The data revealed several characteristic spectral peaks that can be used to make health determinations. The fluorescence peaks are attributed to fluorescent proteins (FPs) and Chlorophyll-a fluorescence. The reflectance peaks can be attributed to Chlorophyll absorption and accessory pigments such as Peridinin and Diadinoxanthin. Each characteristic spectral peak or ‘marker’ allows for observation of each aspect of coral health and hence, simultaneous monitoring of these markers using hyperspectral imaging techniques provides an opportunity to better understand the processes occurring during bleaching and the rates at which they occur relative to one another.

Oceans doi: 10.3390/oceans3040035

Authors: Michael P. Lesser Marc Slattery Keir J. Macartney

Studies on the trophic ecology of scleractinian corals often include stable isotope analyses of tissue and symbiont carbon and nitrogen. These approaches have provided critical insights into the trophic sources and sinks that are essential to understanding larger-scale carbon and nitrogen budgets on coral reefs. While stable isotopes have identified most shallow water (<30 m) corals as mixotrophic, with variable dependencies on autotrophic versus heterotrophic resources, corals in the mesophotic zone (~30–150 m) transition to heterotrophy with increasing depth because of decreased photosynthetic productivity. Recently, these interpretations of the stable isotope data to distinguish between autotrophy and heterotrophy have been criticized because they are confounded by increased nutrients, reverse translocation of photosynthate, and changes in irradiance that do not influence photosynthate translocation. Here we critically examine the studies that support these criticisms and show that they are contextually not relevant to interpreting the transition to heterotrophy in corals from shallow to mesophotic depths. Additionally, new data and a re-analysis of previously published data show that additional information (e.g., skeletal isotopic analysis) improves the interpretation of bulk stable isotope data in determining when a transition from primary dependence on autotrophy to heterotrophy occurs in scleractinian corals.

Oceans doi: 10.3390/oceans3040034

Authors: Putu Liza Kusuma Mustika Kathryn K. High Mochamad Iqbal Herwata Putra Achmad Sahri I Made Jaya Ratha Muhammad Offal Prinanda Firdaus Agung Februanty S. Purnomo Danielle Kreb

Analyses of the spatial and temporal patterns of 26 years of stranding events (1995–2011 and 2012–2021, n = 568) in Indonesia were conducted to improve the country’s stranding response. The Emerging Hot Spot Analysis was used to obtain the spatial and temporal hotspot patterns. A total of 92.4% events were single stranding, while the remaining were of mass stranding events. More stranding events were recorded between 2012 and 2021 in more dispersed locations compared to the previous period. Within the constraints of our sampling limitations, East Kalimantan and Bali were single stranding hotspots and consecutive hotspots. East Java and Sabu-Raijua in East Nusa Tenggara were mass stranding hotspots. Temporally, Raja Ampat (West Papua) experienced a significant increase in case numbers. The presence of active NGOs, individuals or government agencies in some locations might have inflated the numbers of reported cases compared to areas with less active institutions and/or individuals. However, our results still give a good understanding of the progression of Indonesia’s stranding responses and good guidance of resource allocation for the stranding network. Several locations in Indonesia that need more efforts (e.g., more training workshops on rescue and necropsies) have been identified in this paper. Suggestions to improve data collection (including georeferencing tips) have also been included.

Oceans doi: 10.3390/oceans3040033

Authors: Karol Roca-Monge Rocío González-Barrientos Marcela Suárez-Esquivel José David Palacios-Alfaro Laura Castro-Ramírez Mauricio Jiménez-Soto Minor Cordero-Chavarría Daniel García-Párraga Ashley Barratclough Edgardo Moreno Gabriela Hernández-Mora

Age parameters in cetaceans allow examining conservation and studying individuals with growth affection. The age and sexual maturity of 51 stranded Stenella coeruleoalba striped dolphins from the Eastern Tropical Pacific (ETP) of Costa Rica, most suffering brucellosis (95.6%), were assessed. In order to ascertain the dolphins’ ages, we measured the length and growth of dentin-layer group counts (GLGs) and assessed flipper bone radiography without (FBSA) and with a formula (FBF). Sexual maturity was determined through gonadal histology and sexual hormone serum levels. Compared with a model based on S. coeruleoalba ages estimations in other latitudes, the striped dolphin studied displayed deficient growth parameters, with considerable variability in length, teeth, and flippers bone development. Close to 43% (n = 15) of GLGs’ measurements were below the body length average ranges for the predicted age, suggesting developmental abnormalities. Likewise, 34.4% and 31.2% of the dolphins assessed by FBSA and FBF were also below the body length based on age prediction curves, also indicating developmental abnormalities. This information is supported by the poor correlation between GLGs, FBSA, and FBF. Inconsistencies between sexually mature males and females related to GLGs, FBSA, and FBF were evident. Although the different oceanic settings of the ETP, such as contamination, food access, diseases, and other parameters, may influence size variation, our data also suggest that long-lasting debilitating brucellosis may account for detrimental growth in the ETP striped dolphins. Our study highlights the possible deleterious consequences of chronic infectious diseases in the cetacean populations already confronting distressful conditions.

Oceans doi: 10.3390/oceans3040032

Authors: Rebekah Shunmugapandi Shirishkumar Gedam Arun B. Inamdar

Changes in the environmental condition associated with climatic events could potentially influence the PSC dynamics of the regional marine ecosystem. The Indian Ocean dipole (IOD) is one of the critical ocean–atmosphere interactions that affects the climate of the Arabian Sea, and it could be a potential factor influencing the regional PSC distribution. However, the relationship between PSC and IOD remains unclear and less explored. In this study, using the in-situ database acquired from the Arabian Sea, we reparametrized the three−component abundance−based phytoplankton size class model and applied it to reconstructed satellite−derived chlorophyll−a concentration to extract the fractional contribution of phytoplankton size classes to chlorophyll−a concentration. Further, we investigated the influence of IOD on the changes in the biological–physical properties in the Arabian Sea. The results showed that the biological–physical processes in the Arabian Sea are interlinked and the changes in the IOD mode control the physical variables like sea surface temperature (SST), sea surface height (SSH), and mixed layer depth (MLD), which influence the specific PSC abundance. Unprecedented changes in the PSC distribution and physical properties were observed during the extreme positive and negative IOD events, which clearly indicated the potential role of IOD in altering the PSC distribution in the Arabian Sea. This study highlights the impact of extreme climate events on PSC distribution and the need for a better understanding of the associated physical–biological–climate interactions.

Oceans doi: 10.3390/oceans3040031

Authors: Todd L. Schmitt Caroline E. C. Goertz Roderick C. Hobbs Steve Osborn Stacy DiRocco Heidi Bissell William S. Harris

This investigation compared the fatty acid (FA) levels found in erythrocyte (RBC) membranes, plasma, whole blood (WB), and blubber from wild Alaskan (Bristol Bay) belugas (Delphinapterus leucas) (BBB, n = 9) with oceanaria-based belugas (OBB, n = 14) fed a controlled diet consisting of primarily herring (Clupea harengus) and capelin (Mallotus villosus). FA patterns in RBCs, WB, and plasma varied considerably between BBB and OBB animals. Focusing on RBC FA levels of known dietary origin, the OBBs had markedly higher levels of 20:1n9,11 and 22:1n9,11. RBC levels of these fatty acids were 1% and 0.2% in the BBBs, but 8.2% and 4.5%, respectively, in the OBBs (p < 0.05 both). These long-chain mono-unsaturated FAs (LC-MUFAs) are rich in herring and capelin but not in the prey species (i.e., salmonids, smelt, cod, and shrimp) generally available to BBBs. As for the marine omega-3 poly-unsaturated fatty acids [PUFAs; 20:5n3 (eicosapentaenoic acid) and 22:6n3 (docosahexaenoic acid)], the former was higher in the OBBs vs. BBBs (16% vs. 11%, p < 0.05), but the latter was low and similar in both (3.8% vs. 4%). Similar patterns were seen in the other sample types, except that DHA% was higher in BBB than OBB animals in both plasma (12.6% vs. 8.7%) and in blubber (12% vs. 4.9%) (p < 0.05). A physiologically important omega-6 PUFA, 20:4n6 (arachidonic acid) was approximately 2× higher in BBB than OBB within RBC (22% vs. 12%), WB (16% vs. 7%), plasma (11.5% vs. 4.6%) and blubber (4.6% vs. 2.4%), respectively. While blubber FAs have been evaluated historically and relatively easy to procure with biopsy darts in the field, this study proposes that blood-based FAs collected during health assessments or subsistence hunts, especially RBC or WB FAs, may be more convenient to handle using dried blood spot cards (DBS) with limited cold storage and simplifies shipping requirements, and may more accurately reflect tissue FA status.

Oceans doi: 10.3390/oceans3040030

Authors: Ikuko Tomo Catherine M. Kemper

The semi-enclosed environment of the St Vincent Gulf Bioregion and its fauna are impacted by many human activities. Long-term monitoring of cetaceans is vital. Records of collected specimens (173) and those not examined by the South Australian Museum (98 non-specimens) from 2009–2020 were analyzed. Necropsies were carried out on most carcasses using gross, histopathological, and diagnostic assessment of pathogens, organs, and skin lesions. The relative age and circumstance of death were assigned. Baleen whales (five species) and odontocetes (eight species) were studied. Indo-Pacific bottlenose dolphins (Tursiops aduncus) and common dolphins (Delphinus delphis) were frequently recorded and analyzed in detail. Anthropogenic cases were prevalent (21%). Many dolphins (62%) were immature males. Disease (73%) was the most frequently recorded circumstance of death. The most common pathological change was inflammatory disease, including infectious pneumonia. In Indo-Pacific bottlenose dolphins, infectious disease was more prevalent in the greater St Vincent Gulf Bioregion than in the Adelaide Dolphin Sanctuary. Microbe testing confirmed 32 species of bacteria, 2 fungi, and 1 virus. Nematodes and trematodes were recorded throughout the study, sometimes in association with microbes. Toxoplasma gondii was observed in an Indo-Pacific bottlenose dolphin. Severe traumatic injury was recorded in many dolphins, including anthropogenic cases. A tumor (leiomyoma) was described from a single common dolphin. This study provides an important baseline for the future monitoring of emerging infectious and chronic diseases, and anthropogenic threats in the region.

Oceans doi: 10.3390/oceans3030029

Authors: Richard K. F. Unsworth Leanne C. Cullen-Unsworth James N. Hope Benjamin L. H. Jones Richard J. Lilley Hanna K. Nuuttila Beth Williams Nicole E. Esteban

Seagrass meadows commonly reside in shallow sheltered coastal environments which are typically safe havens for mooring boats. There is evidence from around the globe that the use of common swinging chain moorings leads to halos of bare sediment in otherwise productive seagrass. These halos reduce animal abundance and diversity and lead to a loss of the carbon stored within sediments. To protect and enhance seagrass ecosystem services, low-cost simple solutions are required that can solve the problems of boating-based disturbance. In the present novel study, we provide evidence that the simple replacement of mooring chains with rope can significantly reduce damage to sensitive benthic habitats such as seagrass. At three locations across a range of environmental conditions, we provide evidence that well-established moorings constructed from rope do not damage seagrass. Overall, there was a significant effect (F1,756 = 299.46, p < 0.001) of the mooring type and distance from the mooring base. This equates to a 44% increase in seagrass cover within areas around a rope mooring relative to a chain one. Most small boat mooring activity happens within the summer months, therefore large heavy-duty winter mooring systems are not required in many situations, opening opportunities for adapted systems that have a reduced environmental impact. The present study suggests that there is a ready-made, low-technology, low-cost solution already in existence for halting the widespread loss of seagrass from small boat mooring damage and allowing recovery and opportunity for restoration.

Oceans doi: 10.3390/oceans3030028

Authors: Benjamin L. H. Jones Richard K. F. Unsworth Lina M. Nordlund Rohani Ambo-Rappe Yayu A. La Nafie Mary Rose Lopez Susantha Udagedara Leanne C. Cullen-Unsworth

It is widely recognized that humanity is currently facing multiple planetary crises, including the widespread loss of biodiversity and a rapidly changing climate. The impacts of these crises are often far reaching and threaten food security (SDG goal two: zero hunger). Small-scale fisheries are estimated to provide livelihoods for over one hundred million people and sustenance for approximately one billion people but face a plethora of threats and challenges linked to planetary crises. In this multi-country assessment (150 coastal villages across five countries within the Indo-Pacific), household interviews revealed how seagrass meadows are important to small-scale fisheries, particularly as a place to find and collect a reliable source of food. Interviews also revealed that habitat loss and the over-exploitation of these resources are placing people and their food security at risk. This study exposed how dynamic local ecological knowledge can be, uncovering personal opinions and responsibilities that result in the hybridization of knowledge. Here, we demonstrate the importance of using local ecological knowledge to incorporate shared values into management but also highlight that an integrated approach, pairing local and conventional scientific knowledge, is needed urgently if we are to meet the needs of people while simultaneously conserving biodiversity.

Oceans doi: 10.3390/oceans3030027

Authors: Lizabeth Bowen Susan Knowles Kathi Lefebvre Michelle St. Martin Michael Murray Kim Kloecker Daniel Monson Benjamin Weitzman Brenda Ballachey Heather Coletti Shannon Waters Caroline Cummings

An opportunistic investigation into ecosystem instability in Kachemak Bay (KBay), Alaska, has led us to investigate exposure to toxic algae in sea otters. We used gene expression to explore the physiological health of sea otters sampled in KBay in May 2019. We found altered levels of gene transcripts in comparison with reference sea otters from clinically normal, oil-exposed, and nutritionally challenged populations sampled over the past decade. KBay sea otters were markedly divergent from the other groups for five genes, which indicated the involvement of neurological, cardiac, immune, and detoxification systems. Further, analyses of urine and fecal samples detected domoic acid in the KBay sea otters. In combination, these results may point to chronic, low-level exposure to an algal toxin, such as domoic acid. With a warming climate, the frequency and severity of harmful algal blooms in marine environments is anticipated to increase, and novel molecular technologies to detect sublethal or chronic exposure to algal toxins will help provide an early warning of threats to the stability of populations and ecosystems.