Oceans

Toxic dinoflagellate blooms and microplastics are widespread coastal pollutants. In this study, the scallop, Argopecten irradians, was selected as an experimental organism to systematically investigate the single and combined toxic effects of polystyrene (PS) and the toxic dinoflagellate, Alexandrium pacificum. The results showed that both PS and algal cells could be ingested by A. irradians. The survival rate of A. irradians remained above 90% in both the single and combined treatment groups, indicating that 1 mg/L PS and 1500 cells/mL A. pacificum cells did not pose a serious threat to scallop survival in the short term. However, CAT, SOD, and GSH-ST activities, as well as MDA content, were all elevated in the combined treatment group. Transcriptomic analysis further revealed that A. pacificum primarily affected immune-related pathways, whereas PS might interfere with endocrine function through the release of additives. Combined exposure to PS and A. pacificum induced more complex synergistic effects, reflected in the metabolic stress of exogenous substances, and the disruption of developmental and homeostasis regulatory pathways. This study provides important theoretical support for assessing the threats posed by composite coastal pollution to aquaculture and marine ecological security. Full article

The reproductive cycle of the European clam Ruditapes decussatus reared in suspended double-net trays in the Oualidia Lagoon was investigated from October 2017 to February 2019. This study aimed to characterize gonadal development through histological analysis, gonadal index assessment, and the biochemical composition of key macromolecules (proteins, lipids, and carbohydrates) over an annual cycle. The results revealed that R. decussatus undergoes a prolonged spawning period from April to December, with a peak in October when 100% of the population reached the maturation stage (stage IIIA). A sexual rest phase was observed between November 2017 and December 2017. An overall sex ratio of 1:0.8 was observed, indicating a slight female bias, with no significant deviations. Statistical analyses highlighted a correlation between the gonadal index and seawater temperature, suggesting that temperature plays a crucial role in regulating reproductive activity. Biochemical analyses showed that proteins were the predominant macromolecule in clam tissues, followed by lipids and carbohydrates. Seasonal variations in biochemical composition were observed; however, no direct correlation was found between biochemical compound levels and the gonadal index (p > 0.05). These findings provide valuable insights into the reproductive biology of R. decussatus under suspended aquaculture conditions, contributing to improved management and optimization of farming practices. Full article

The Atlantic bluefin tuna (Thunnus thynnus) is a high-value species subject to strict catch quotas and seasonal closures in the Mediterranean Sea. However, detecting illegal, unreported, and unregulated fishing remains challenging, particularly for small-scale activities. The aim of this study is to investigate whether citizen-reported strandings of tuna remains along Italian coasts can provide potential indirect indications of illegal fishing activities. To address this question, we collected and verified photographic records of stranded tuna remains (e.g., skulls, vertebral elements, complete specimens) reported on social networks. A similar search was conducted for two other conspicuous fishes, the ‘dusky grouper’ (Epinephelus marginatus) and the ‘greater amberjack’ (Seriola dumerili), as controls. Thirty-two strandings of tuna remains were recorded, with no records of amberjacks and only one of dusky grouper. Most strandings involved tuna heads or neurocrania, some of which showed clear mechanical cuts indicating post-capture processing. Several remains were older and degraded, suggesting long-term persistence in the sea. Overall, our results indicate that citizen-reported strandings could provide low-cost, spatially broad potential indications of discards resulting from illegal fishing activities. Wider adoption of standardised public reporting could not only engage the public in marine conservation, but also provide valuable data for policymakers tackling illegal fishing and complement traditional fisheries monitoring. Full article

Underwater imaging suffers from significant degradation due to scattering by suspended particles, selective absorption by the medium, and depth-dependent noise, leading to issues such as contrast reduction, color distortion, and blurring. Existing enhancement methods typically address only one aspect of these problems, relying on unrealistic assumptions of uniform noise, and fail to jointly handle the spatially heterogeneous noise and spectral channel attenuation. To address these challenges, we propose the variational-based spatial–spectral joint enhancement method (VSJE). This method is based on the physical principles of underwater optical imaging and constructs a depth-aware noise heterogeneity model to accurately capture the differences in noise intensity between near and far regions. Additionally, we propose a channel-sensitive adaptive regularization mechanism based on multidimensional statistics to accommodate the spectral attenuation characteristics of the red, green, and blue channels. A unified variational energy function is then formulated to integrate noise suppression, data fidelity, and color consistency constraints within a collaborative optimization framework, where the depth-aware noise model and channel-sensitive regularization serve as the core adaptive components of the variational formulation. This design enables the joint restoration of multidimensional degradation in underwater images by leveraging the variational framework’s capability to balance multiple enhancement objectives in a mathematically rigorous manner. Experimental results using the UIEBD-VAL dataset demonstrate that VSJE achieves a URanker score of 2.4651 and a UICM score of 9.0740, representing a 30.9% improvement over the state-of-the-art method GDCP in the URanker metric—a key indicator for evaluating the overall visual quality of underwater images. VSJE exhibits superior performance in metrics related to color uniformity (UICM), perceptual quality (CNNIQA, PAQ2PIQ), and overall visual ranking (URanker). Full article

The deep sea is often depicted as a barren environment. Using the abyssal plain as a baseline system characterized by high pressure, extreme nutrient limitation, and slow growth rates, this review contrasts these conditions with specialized habitats that serve as oases of life such as whale falls, cold seeps, and hydrothermal vents. These environments retain the high-pressure characteristic of deep-sea habitats, but other unique environmental factors select for organisms with distinct life-history strategies and growth rates. This review examines the environmental constraints, organism physiological adaptations, and life-history strategies that define each habitat. Through synthesizing these factors, we identify patterns that influence not only growth and succession, but broader ecosystem vulnerability and resilience, defined here as the capacity of these communities to recover from disturbance. By evaluating how biological traits contribute to resilience across the four habitats in response to specific environmental constraints, this comparative framework identifies trade-offs between growth specialization and habitat stability. Understanding these environmental factors is critical in evaluating the resilience of these habitats to growing anthropogenic disturbances and determining future directions of study. This review concludes that while hydrostatic pressure and temperature impose fundamental metabolic constraints, nutrient availability and habitat stability are the primary determinants of organismal growth rates and life-history strategies. In the context of each ecosystem, both these variables can play a large role in the ability and time to recover from disturbance and may be good indicators of resilience at both a community and an organismal level. Consequently, slow-growing, long-lived fauna may possess far lower intrinsic resilience to anthropogenic disturbance compared to rapidly growing organisms with shorter life histories. Varying resilience of these habitats may necessitate habitat-specific strategies for assessment and protection. Full article

Knowledge of deep-sea amphipods remains much more limited compared to that of shallow-water or more accessible marine habitats, although there has been an increasing scientific interest in recent decades. Deep-sea amphipods are mainly scavengers and detritivores, playing a role in organic matter recycling; however, their species richness may be underestimated, especially in understudied realms like the deep Mediterranean Sea. Long-term monitoring data are limited, hindering understanding of trends or human impacts. The present work aims to address this gap. In a previous study (1993–1996), twenty-two species of amphipods were identified from samples collected at depths between 734 and 1558 m along the Israeli coast. After twenty years, 16 sites were sampled in 2013 at depths ranging from 198 to 1812 m. Amphipod assemblage and its bathymetric distribution were analyzed to enhance knowledge of the taxon’s occurrence. Full article

Under the requirements of the EU Nature Restoration Regulation, significant investment in the restoration of marine and coastal ecosystems will be necessary in EU Member States. A certain level of knowledge among the population will be required to ensure authorities have the required social license to pursue marine ecosystem restoration activities, and awareness raising campaigns will likely be a part of the body of actions taking place to support the delivery of the EU Nature Restoration Regulation. This survey assesses the baseline awareness, attitudes and support for marine and coastal restoration amongst the Irish adult population. Relatively low levels of awareness of both restoration initiatives and the regulation are documented, with approximately 15% of respondents aware of restoration activities and 19% aware of the regulation. While distance to the coast isn’t always strongly correlated with awareness and support, connection to the marine—represented by visiting the coast and being concerned about the marine environment—is strongly correlated with these metrics. The results indicate that information campaigns around marine and coastal restoration should attempt to highlight the benefits society receives from the marine and coastal environment and foster a sense of connection with it. Full article

Although previous studies composited response of sea surface temperature (SST) to typhoon sea surface wind (SSW) forcing around typhoon center, how SST responded spatiotemporally along the typhoon track over the ocean remains unclear. Through Empirical Orthogonal Function (EOF) analysis, several isolated typhoons in the Western North Pacific (WNP) from 2021 to 2024 were investigated. Two SSW forcing modes and two SST response modes were identified. The first SSW mode spatially reflects the overall distribution of SSW along the track, centering at its maturation position. And the first SST mode exhibits a high spatial correlation ($\left|R\right|>0.85$) with this SSW mode. The second SSW mode displays a distinct track-long scale dipole pattern along the path of the typhoon, representing its intensity variation during the “development–maturation–decay” lifecycle. Similarly, the second SST response mode shows a significant but lower correlation with this second SSW mode. Both corresponding SST response modes typically lag behind their respective wind-forcing by approximately 2 to 4 days, indicating that these SST response modes are direct reactions to SSW forcing. These cases implies that two track-long scale SSW modes are generally present during the lifecycle of typhoons and that their corresponding SST responses are dominated accordingly. Full article

We use 29 years of altimeter-derived sea level anomalies and geostrophic velocities (1993–2021) from the Copernicus Marine Service to identify the Mexican Coastal Current (MCC) and to examine how it interacts with the coastline. Variance-ellipse and empirical orthogonal function analyses isolate a narrow alongshore jet with a mean width of about 95 km and average speeds near 0.3 m ${\mathrm{s}}^{-1}$ that reverses direction semiannually: poleward in June and July and equatorward in the rest of the year. When the MCC impinges on broad concavities in the coast, the boundary layer separates, forming recirculation cells that intensify and detach as coherent eddies. These near-shore eddies have similar radii (from ∼30 km) and relative vorticity of $\pm 0.5\times {10}^{-5}$${\mathrm{s}}^{-1}$ at the beginning of their generation, and they propagate offshore once the current weakens. A simple numerical model reproduces the observed behavior and suggests that eddy formation is controlled by flow separation rather than generic instability. The semiannual change in direction of the MCC indicate a link with the larger-scale North Equatorial Countercurrent and Costa Rica Coastal Current systems of the eastern tropical Pacific. Full article

Changes in climate and ocean pollution has prioritized monitoring of ocean surface behavior. Ocean drifters, which are floating sensors that record position and velocity, help track ocean dynamics. However, environmental events such as oil spills can cause abnormal behavior, making anomaly detection critical. Unsupervised learning, combined with deep learning and advanced data handling, is used to detect unusual behavior more accurately on the NOAA Global Drifter Program dataset, focusing on regions of the West Coast and the Mexican Gulf, for time periods spanning 2010 and 2024. Using Density-Based Spatial Clustering of Applications with Noise (DBSCAN), pseudo-labels of anomalies are generated to train both a one-dimensional Convolutional Neural Network (CNN) and a Long Short-Term Memory (LSTM) network. The results of the two models are then compared with bootstrapping with block shuffling, as well as 10 trials with bar chart summaries. The results show nuance, with models outperforming the other in different contexts. Between the four spatiotemporal domains, a difference in the increasing rate of anomalies is found, showing the relevance of the suggested pipeline. Beyond detection, data reliability and efficiency are addressed: a RAID-inspired recovery method reconstructs missing data, while delta encoding and gzip compression cut storage and transmission costs. This framework enhances anomaly detection, ensures reliable recovery, and reduces energy consumption, thereby providing a sustainable system for timely environmental monitoring. Full article

The open ocean cage aquaculture system is facing considerable challenges with disease outbreaks resulting from over-farming and the rise of resistance to antimicrobial treatment. However, the environmental consequences of antibiotic usage, including ecological contamination and the acceleration of antimicrobial resistance, underscore the urgent need for sustainable alternatives in aquaculture disease management. Lipopeptides, which are a compound that can be produced by marine bacteria such as Bacillus amyloliquefaciens or Bacillus subtilis, could represent a new solution. This review article comprehensively evaluates the feasibility of marine bacterial lipopeptides for sustainable disease management in open sea cage aquaculture. Lipopeptides, including surfactins, fengycins, iturins, and the clinically used daptomycin, have notable antiviral, antifungal, and antimicrobial properties, and can have positive effects on the immune system. Notably, lipopeptides have a remarkable antioxidant profile and excellent free radical scavenging ability, making them interesting candidates for improving disease resistance in fish relating to oxidative stress. The surfactins and iturins have amphiphilic structure and can destabilize pathogen cell membranes, inhibit biofilm formation and elicit host immune responses. This represents a paradigm shift in targeting multiple pathogens of aquaculture like Vibrio spp. and Aeromonas spp. Surfactins and iturins show broad-spectrum activity, while fengycins are selectively active against fungal threats. Daptomycin, which is primarily derived from Streptomyces, demonstrates the potential of the lipopeptide class to be developed therapeutically, which is something that tends to be overlooked. Unlike synthetic antibiotics, they are also biodegradable; therefore, there is much less environmental impact from lipopeptides. The complexity of the structure may have also some impact on the rate of development of resistance, if any. Their commercialization is possible; however, the main hurdles that need to be solved to improve aquaculture are the biologically scalable production, the economically viable purification, and the stability for practical application at sea. Integrating lipopeptides into disease management systems could also ensure the sustainability of open ocean cage aquaculture and reduce unnecessary antibiotic application. Full article

Monitoring trace metals in commercially important fish species provides an early warning of anthropogenic contamination and potential risk to consumers. This study semi-quantified and quantified essential, non-essential, and toxic elements in the muscle of wild meagre (Argyrosomus regius) captured in the Tagus estuary (Portugal), which is used as a nursery and spawning aggregation area. Dry muscle was microwave-digested and analyzed using inductively coupled plasma–optical emission spectroscopy. Semi-quantified screening detected Al, B, Ca, Fe, K, Mg, Na, P, S, Si, Sr, and Ti, and eight elements were determined using multielement calibration (As, Cr, Cu, Hg, Mn, Ni, Se, and Zn); Cd, Pb (toxic elements), Co, and Mo were not detected in this study. Arsenic was detected in all individuals, with a minimum value of 0.348 mg/kg wet weight. A mercury level above the European Commission regulatory limit (0.5 mg/kg wet weight) was only detected in one individual, corresponding to 2% of the samples. Although other metals remain well below regulatory limits, continued biomonitoring is recommended to track temporal trends and safeguard seafood safety in transitional coastal systems, which is important for commercially relevant fish species. Full article

In early 2025, the Jason-3 satellite’s orbit shifted from an “interleaved” to a tandem configuration with Sentinel-6A, and its Geophysical Data Records (GDR) were upgraded from Version F to G. This study evaluated GDR-G via eight processing approaches, using Jason-3’s last six GDR-F cycles (#394–#399) and first six GDR-G cycles (#501–#506), integrating histogram/geographical distribution analyses of Sea Surface Height Anomaly (SSHA), Significant Wave Height (SWH), Wind Speed (WS), and multi-method validation (e.g., self-cross-calibration). Key findings include the following: GDR-G had significantly lower SSHA noise than GDR-F, with up to ~4 cm SSHA bias from different retrackers/corrections; Adaptive retracker + 3D Sea State Bias (SSB) correction achieved optimal accuracy. Adaptive retracker’s SWH/WS anomalies linked to invalid MLE4 results and non-Brownian waveforms (coastal/sea ice). A detrending method was proposed, and the 41-point Lanczos window was optimal for smoothing. The results from the “detrending method” were consistent with the results based on the SSHA spectrum and classic self-cross-calibration methods. A ~5 mm drop was observed in Jason-3 GDR-G MLE4 baseline SSHA, probably caused by GDR upgrade or geographic sampling mismatch, while Sentinel-6A’s GDR-G upgrade might induce ~1 cm jump. The jumps along with GDR version upgrade highlighted the value of timely in situ absolute calibration. Full article

Citizen science approaches for monitoring, and even restoring, coral reefs have grown in popularity though tend to be restricted to those who have taken courses that expose them to the relevant methodologies. Now that cheap (~10 USD), waterproof pouches for smart phones are widely available, there is the potential for mass acquisition of coral reef images by non-scientists. Furthermore, with the emergence of better machine-learning-based image classification approaches, high-quality data can be extracted from low-resolution images (provided that key benthic organisms, namely corals, other invertebrates, & algae, can be distinguished). To determine whether informally captured images could yield comparable ecological data to point-intercept + photo-quadrat surveys conducted by highly proficient research divers, we trained an artificial intelligence (AI), CoralNet, with images taken before and during a bleaching event in 2015 in Chagos (Indian Ocean). The overall percent coral covers of the formal, “gold standard” method and the informal, “tourist diver” approach of 38.7 and 35.1%, respectively, were within ~10% of one another; coral bleaching percentages of 30.5 and 31.8%, respectively, were statistically comparable. Although the AI was prone to classifying bleached corals as healthy in ~one-third of cases, the fact that these data could be collected by someone with no knowledge of coral reef ecology might justify this approach in areas where divers or snorkelers have access to waterproof cameras and are keen to document coral reef condition. Full article

Holothuroids play a vital role in nutrient cycling and bioturbation to enhance the marine ecosystem. They enhance the biodiversity for various symbiotic marine organisms by providing essential shelter and spawning grounds. This review focuses on the Class Holothuroidea (Phylum Echinodermata) in Indian waters, encompassing a total of 187 species organized into 7 orders and 21 families. Notably, the order Holothuriida represents the largest proportion of species, accounting for 27%. These species are well-distributed across India, with the Andaman and Nicobar Islands exhibiting the highest level of species richness (107 species), followed by the East Coast (102 species), Lakshadweep (39 species), and the West Coast (34 species). Species diversity was assessed using the Shannon–Weiner diversity index. Results indicate that the Andaman and Nicobar Islands (H’ = 2.23) and the West Coast (H’ = 2.14) demonstrate the highest levels of diversity. This review provides a comprehensive and precise inventory of all species of Holothuroidea reported in Indian waters, which is provided to facilitate understanding of the reported species, their systematics, and distribution. In addition, a significant insight for both conservation and management of sea cucumbers in India has also been provided. Full article

Τhe trophic ecology of Pterois miles in the Mediterranean Sea was performed by integrating data from stomach contents (SCA) and stable isotopes analyses (SIA), based on samples caught off the Greek island of Rhodes, SE, Aegean Sea, for the first time. This combined approach provides information on ingested (SCA) and assimilated (SIA) food and thus allows for the depiction of predator–prey relationships. Specimens of devil firefish, including both juveniles and adults (total length of analyzed specimens spanned from 11.40 to 31.50 cm), were collected from different sites around Rhodes. Their diet consisted of bony fish, cephalopods, crustaceans, and gastropods. The δ¹³C and δ¹⁵N values ranged from −18.0 ‰ to −14.4 ‰ and from 7.2 ‰ to 9.2 ‰, respectively. SIA data allowed for the estimation of the trophic position of devil firefish from Rhodes Island, which showed a mean value of 3.1 ± 0.6 and confirms that the species primarily relies on a benthic baseline. Further, our isotopic values approach those obtained in North Carolina and Bermuda, confirming its role as a mesopredator in the Mediterranean benthic food webs. Although preliminary, such results can provide an important baseline for future investigations on the species and the potential impact on the Mediterranean food webs. Full article

Cape Town, South Africa, experiences coastal upwelling during austral summer. In this study, the effects of kinematic and thermal ‘roughness’ on wind stress are analyzed using 5–25 km resolution multi-satellite and coupled reanalysis datasets in the period 2010–2024. Average conditions for austral summer (December–February) are calculated to identify east–west gradients in sensible heat flux, wave height, and equatorward winds and to assess their consequences for the drag coefficient, wind-driven Ekman transport, and entrainment over the shelf from 16.9 to 18.7° E, north of Cape Town (33.7° S). Statistical and numerical outcomes are compared for austral summer and during active coastal upwelling in January 2018 with chlorophyll concentrations > 3 mg/m³. A subtropical anticyclone generated shallow equatorward winds next to a wind shadow north of Cape Town. Sharp cross-shore gradients in momentum flux were amplified by shoreward reductions in sensible heat flux and wave height, which suppressed the drag coefficient 10-fold. The inclusion of kinematic and thermal roughness in wind stress calculations results in a higher average cyclonic curl (−2.4 × 10⁻⁶ N/m³), which translates into vertical entrainment > 3 m/day at 33.7° S, 18° E. The research links coastal upwelling leeward of a mountainous cape with cross-shore gradients in air–sea fluxes that support recirculation and phytoplankton blooms during austral summer. Full article

Two new species of free-living marine nematodes were collected in the Yellow Sea, China, and they are described herein as Actinonema sinica sp. nov. and Comesoma zhangi sp. nov. Actinonema sinica sp. nov. is characterized by short cephalic setae; lateral differentiation consisting of a row of longitudinal sclerotized bars and beginning at the level of anterior third of the pharyngeal region; horn-shaped telamons; a curved rod-shaped gubernaculum; and an elongate conical tail with a smooth, pointed tip. Comesoma zhangi sp. nov. is characterized by long, thick cephalic setae, reaching up to 28 µm in length; a cup-shaped buccal cavity lacking a tooth and narrowing posteriorly with small projections; an amphidial fovea with two turns; slender, arcuate spicules 2.6 times the cloacal body diameter in length, lacking a proximal capitulum; a plate-like gubernaculum without apophysis; and the absence of precloacal supplements. Updated keys to the valid species of the genus Actinonema and the genus Comesoma are provided. A comparative morphological table of all currently accepted species of Comesoma is also provided. Full article

The Mauritanian–Senegalese Coastal Upwelling exhibits strong interannual variability, which has been found to be driven by El Niño-Southern Oscillation (ENSO). In addition, ENSO has been shown to be triggered by the Indian Ocean and Atlantic Sea Surface Temperature (SST) variability. Nevertheless, how all these basins impact on the upwelling predictability has not been analyzed so far. Using a satellite product of surface chlorophyll-a as a proxy of marine productivity, this work makes an assessment of the predictability of the Mauritanian–Senegalese Coastal Upwelling marine ecosystem. Different statistical approaches are used to evaluate the relative contribution of the tropical basins, including the Pacific, Indian, equatorial and Tropical North Atlantic SSTs. The results indicate that although most of the upwelling variability stands for ENSO, the Atlantic contributions play an important role in shaping the seasonal prediction skill. These results may have strong implications for fisheries and marine ecosystem management in the region. Full article