To our knowledge, this study provides the first microscopic evidence of symbiotic association between Geloina expansa and endosymbiotic dinoflagellates (zooxanthellae). Mangrove ecosystems, recognized for their ecological complexity and biodiversity, host numerous interactions, yet this symbiotic association with Symbiodiniaceae has not been previously documented. The presence of Symbiodiniaceae in the mantle and gill tissues of G. expansa represents a previously undocumented association in mangrove clams and provides a foundation for future investigations into its ecological and physiological significance. By revealing a previously unrecognized clam–algae association, this study emphasizes the importance of investigating symbiotic relationships that influence ecosystem structure, function, and conservation value.
The Bay of Bengal (BoB) has a major influence on the climate and hydrodynamics of South Asia, where complex interactions among tides, waves, and currents pose persistent challenges for coastal communities in Bangladesh. Despite the critical need for accurate regional hydrodynamic characterization, existing modeling studies have not fully addressed the simultaneous calibration and validation of water levels, significant wave heights, and current velocities within a unified coupled framework. This study developed a two-dimensional coupled wave-hydrodynamic model for the northern BoB using the Delft3D modeling suite, incorporating high-resolution bathymetry, river discharge, tidal boundary conditions, and spatiotemporally varying wind and wave forcing. The model was calibrated and validated against observed tide levels, significant wave heights, and current velocities at multiple coastal stations, yielding Pearson’s correlation coefficients of 0.79–0.99 and Nash–Sutcliffe efficiency values of 0.72–0.99 across all parameters. A year-long simulation revealed substantial spatial variability in coastal hydrodynamics, with current magnitudes strongly modulated by tidal phase, pronounced tidal asymmetry near major estuarine systems, and elevated wave activity along exposed southeastern coastal sectors during the southwest monsoon. The model accurately reproduced semi-diurnal tidal patterns, dominant current directions, and seasonal wave characteristics across contrasting coastal environments. These findings demonstrate that the coupled model serves as a robust regional baseline for understanding tide-wave-current interactions along the Bangladesh coast, with direct implications for coastal management, storm surge prediction, disaster preparedness, and long-term climate change impact assessment in this vulnerable region.
Zooplankton form the trophic link between marine primary production and higher consumers and play a central role in carbon export, making reliable estimates of their abundance essential for understanding marine ecosystem dynamics in a changing world. However, zooplankton datasets are frequently employ different sampling depth intervals (i.e., bin widths, defined as the vertical extent sampled per tow). Because wider bins integrate over larger water volumes, they yield abundance estimates with differing precision which, if unaccounted for, introduce heteroscedasticity that can bias inference. We compared statistical frameworks for modeling calanoid copepod abundance in waters surrounding the Kerguelen Islands as a function of temperature and mean depth. Specifically, we evaluated a linear model fitted to log-transformed response data and generalized linear models (GLMs) assuming log-normal, Gamma, and inverse Gaussian error distributions. Model selection based on generalized Akaike information criterion (GAIC) identified the inverse Gaussian GLM as the best-supported framework (GAIC = − 3068.25). We then extended that model by explicitly parameterizing dispersion as a function of normalized bin width to account for heterogeneity in measurement precision. This approach addresses an important but often overlooked source of heteroscedasticity in marine ecological datasets. Incorporating a bin-width-dependent dispersion structure improved model fit (GAIC decreased from − 3068.25 to − 3084.61) and altered covariate inference. The temperature-by-depth interaction was statistically significant in the constant-dispersion model but became non-significant when dispersion heterogeneity was included (p = 0.0023 to 0.0657), whereas depth remained a robust predictor. For datasets with strictly positive, strongly right-skewed abundance and sampling protocols that create predictable differences in observation precision, direct distributional models with an explicit dispersion component may yield more reliable inference than a log-transformed Gaussian model. This conclusion is limited to the four candidate frameworks and the single-year dataset evaluated here and requires validation in other regions, years, and taxa.
The impact of ocean acidification (OA) on seawater carbonate chemistry, particularly on the aragonite saturation state (Ωarag), is inadequately understood in the Gulf of Mannar (GoM) and Palk Bay (PB). In this study, we analyzed the spatial and temporal variability of Ωarag to pinpoint potential ocean acidification hotspots within these two ecologically critical coastal habitats along the southeastern coast of India. A pilot study was conducted over 24 locations during 2023–2024. The findings reveal that PB had a higher mean pH (8.33 ± 0.06) than GoM (8.08 ± 0.02). In GoM, Ωarag values were lower, at 2.82 ± 0.20, indicating that calcification conditions were not adequate. In PB, it reached 3.22 ± 0.57, which means that conditions for calcifying organisms were favourable. Seasonal variability in Ωarag was primarily controlled by pH, carbonate ion concentration, pCO2, and monsoonal hydrographic processes Seasonal patterns corroborated that these conditions were modulated by both anthropogenic activities and natural processes. During the Northeast and Southwest monsoons, there were significant drops in Ωarag that matched changes in important biogeochemical indices. Overall, these results reveal that PB experiences greater variability in Seawater carbonate chemistry, while GoM exhibits relatively stable but slightly lower carbonate saturation. Pearson correlation and Structural Equation Modelling further demonstrated that pH and carbonate ion concentration positively influenced Ωarag, whereas pCO2 and Revelle factor showed negative relationships. The findings enunciate that GoM is more vulnerable to ocean acidification than PB and emphasize the value of Ωarag as a sensitive indicator for detecting emerging acidification hotspots in coastal waters. It also emphasizes the importance of regular monitoring of OA parameters in these regions to protect these critical ecosystems and their associated services.
Marine bacteria are recognized as predominant renewable resources of bioactive compounds as they possess unique biosynthetic gene clusters (BGCs) responsible for the production of bioactive molecules. The number and the type of BGCs can vary among different bacterial species. Therefore, in this in silico study, the BGCs of different marine bacterial species were analysed using the online gene mining platform AntiSMASH. The result revealed that every bacterial species can produce a specific group of compounds. However, the production of the lipopeptide fengycin was common among the bacterial species and was found in 86.66
Surface Layer Temperature Inversion (SLTI), a warm layer between the surface and subsurface colder waters, is a significant oceanographic feature that has a profound impact on the oceanic acoustic propagation. Strong inversions are observed in northern BoB and in the South Eastern Arabian Sea (SEAS) with a temperature difference of 5 °C and 3 °C, respectively. Here, we identify and characterise the prominent SLTI regions in the North Indian Ocean. Representative temperature profiles that have been measured from different regions of the North Indian Ocean are selected and classified into six types with respect to the dominant causative factors of SLTI. Then, the acoustic propagation in the surface layer is examined in the presence and absence of SLTI in terms of sonic layer depth, cut-off frequency and limiting ray angle. For the representative profiles analysed in this study, except at stations, where the dominant causative factor of SLTI is river water influx, the sonic layer depth (SLD) increases. Acoustic implications of SLTI are also examined utilizing the ray model (cTraceo). In cases where the dominant cause of SLTI is freshwater influx, the sonic layer shoals and the acoustic waves insonify comparatively farther and deeper regions during non-inversion. This study addresses the variability of acoustic propagation all along the North Indian Ocean driven by SLTI.
Marine microbial enzymes exhibit superior biochemical properties compared to their terrestrial counterparts due to adaptations to extreme marine conditions, including high salinity, temperature fluctuations, hydrostatic pressure, and nutrient limitation. These adaptations confer enhanced thermostability, halotolerance, psychrophilicity, and catalytic efficiency. This review evaluates their biomedical potential in managing chronic inflammation, malignancies, and antimicrobial resistance (AMR) associated with chronic infections. Enzymes such as superoxide dismutase (SOD), laccase, and chitinase mitigate oxidative stress and inflammatory signaling by modulating superoxide radicals and key mediators (NF-κB, MAPK, and pro-inflammatory cytokines), demonstrating promise for the treatment of autoimmune, neuroinflammatory, and metabolic disorders. In oncology, marine L-asparaginase and L-glutaminase exploit tumor-specific amino acid auxotrophies, while marine proteases and lipases target extracellular matrix remodeling and selective oxidative pathways. For AMR, chitinases, serine/alkaline proteases, and alginate lyases disrupt biofilm extracellular polymeric substances, achieving 60–69
The enormous wind stress associated with a cyclone will induce strong mixing in the upper ocean. Mixing between the warm mixed layer water and the colder thermocline water can significantly reduce the Sea Surface Temperature (SST) and, in turn, heat transfer across the air-sea interface. The enhanced mixed layer cooling and the reduction in the enthalpy fluxes may finally lead to the weakening of the cyclone. Hence, understanding the mechanisms behind mixed layer cooling and the SST feedback between the ocean and cyclones is essential for intensity prediction. The present study attempts to understand the oceanic process behind the mixed layer cooling during the depression stage of the cyclone ‘Nanauk’ in the Arabian Sea (AS). In situ observations from the moored buoy at eastcentral AS, near the cyclone track, are used to understand the temporal variability of mixed layer temperature, mixed layer depth (MLD), and the Depth of 26 °C (D26 °C) isotherm. The one-dimensional mixed layer model PWP is used to simulate temperature and MLD variability during the direct wind forcing period. The model simulations and observations are consistent during the initial phase of the forcing period. The present study shows that even though wind stress during the depression stage of a cyclonic storm is weaker, entrainment mixing could significantly contribute to the mixed layer cooling. The elevated temperature gradient at the mixed layer base, a typical seasonal characteristic of AS during the monsoon onset phase, was sufficient to facilitate enhanced vertical turbulent entrainment mixing in the AS.
Abstract Thisvestigates the anthropogenic footprint on a coastal marine environment near the Istrian coast (Northern Adriatic Sea) through a scientific diving field campaign conducted in September 2025. The investigation aimed to evaluate local seawater quality by combining onsite hydrochemical measurements with targeted analyses of trace metal elements (TME) and linear alkylbenzene sulfonates (LAS) as indicators of maritime and touristic activities. Ambient hydrochemical parameters (pH: 8.06 ± 0.07, absolute salinity 39.3 ± 0.5 g/kg, redox potential 441.5 ± 21.5 mV) were found to be stable and typical for Adriatic seawater. Principal component analysis (PCA) of TME data revealed two distinct element groups: a geogenic/corrosive Fe–Mn–Ni cluster related to local lithology and an Al-Cd–Cu–Zn group related to maritime activities. LAS analyses revealed a severe localized hotspot at a submarine sewage effluent (≈1469.3 ppb), alongside a consistent low-level background signal across all other sites (≈ 5 ppb). A methodological evaluation highlighted the robustness of the overall sampling and analytical setup, with specific recommendations for future expeditions.
Mauritius, with one of the largest Exclusive Economic Zones in the Western Indian Ocean, hosts rich yet underexplored marine bioresources, including edible seaweeds. Lagoon-based aquaculture systems, such as the floating-cage fish farm at Pointe-aux-Feuilles, are recognized as environments that may experience localized nutrient enrichment and support abundant macroalgal growth, thereby offering a strategic foundation for the implementation of Integrated Multi-Trophic Aquaculture (IMTA) and advancing sustainable blue economy development. This study evaluated the antioxidant profiles of seven edible seaweeds colonizing aquaculture structures using validated Association of Official Analytical Chemists (AOAC) and spectrophotometric methods. Species-specific assessments of ascorbic acid, total phenolics, flavonoids, β-carotene chlorophyll a, and monomeric anthocyanins revealed significant interspecific variation (p < 0.05). Ulva torta (tubular form) exhibited high Vitamin C content (640 ± 25.6 mg/kg FW), indicating strong nutritional potential. Padina santae-crucis (lineage #2) showed the highest phenolic (22.25 ± 5.74 mg/kg FW) and flavonoid content (398.8 ± 14.6 mg/kg FW). Red seaweed Dasya corymbifera and Gracilaria rangiferina were enriched in β-carotene (28.18 ± 2.22 mg/kg FW) and anthocyanins (0.301 ± 0.003 mg/kg FW), while Dasya corymbifera had the highest chlorophyll a content (24.00 ± 0.05 mg/kg FW). These results demonstrate the remarkable nutritional and functional value of native Mauritian seaweeds and their potential for sustainable food systems, nutraceutical development, and blue bioeconomy innovation. Further work should examine seasonal variability and health effects to support wider application.
Length–weight relationship (LWR) analysis is a fundamental tool for assessing growth patterns, population health, and ecological status of fish species. This study examined the relationship between body length and weight, size–frequency distribution, and relative condition factor of four commercially important pelagic fishes viz. Gazza minuta, Rastrelliger kanagurta, Decapterus russelli, and Sardinella gibbosa from the coastal waters of Terengganu, Malaysia, where LWR information remains limited. Fish samples were collected using purse seine gear fitted with a 1.0-inch mesh size. The LWR parameters were estimated using linear regression analysis after log transformation of length and weight data. The maximum total lengths recorded were 134 mm for G. minuta, 240 mm for R. kanagurta, 219 mm for D. russelli, and 185 mm for S. gibbosa. The estimated growth coefficient (b) for G. minuta was 2.98, reflecting negative allometric growth, whereas R. kanagurta, D. russelli, and S. gibbosa exhibited positive allometric growth with b values of 3.29, 3.10, and 3.11, respectively. The mean relative condition factor (Kn) for G. minuta was low (0.84 ± 0.01), indicating suboptimal physiological condition. In contrast, R. kanagurta, D. russelli, and S. gibbosa showed Kn values close to or exceeding unity (1.14 ± 0.01, 1.04 ± 0.01, and 1.04 ± 0.01), suggesting favourable health conditions. These results provide baseline biological information that can support fisheries management and conservation strategies for small pelagic resources in Terengganu waters.
Caribbean coral reefs have experienced long-term declines in coral cover, structural complexity, and ecological function, yet many local reef systems remain underrepresented in sustained monitoring programs. This study presents a citizen science–generated site-level monitoring dataset for five fringing reef sites around Isla Solarte, Bocas del Toro, Panama, collected between 2023 and 2025. The objective was to establish a reproducible monitoring framework and describe reef conditions across these sites using standardized surveys. Trained citizen scientists collected data on benthic composition, coral condition, maximum relief, and fish assemblages. Fish surveys were developed with close reference to AGRRA methods, while benthic surveys used a point-intercept approach informed by standardized reef-monitoring principles and AGRRA coral-condition terminology. Across the monitored sites, surveys documented low hard coral cover, substantial algal cover, variable sponge and abiotic substrate cover, and significant site-level variation in benthic composition. Coral-condition observations recorded healthy, degraded, bleaching-related, disease-related, and interaction categories, while fish surveys documented variation in fish-group abundance. Bleaching/paling observations were higher in 2023 than in later survey years, providing temporal context for interpreting the dataset during the fourth global coral bleaching event. These data provide a site-specific reference for evaluating future changes in reef condition, coral–algal dynamics, structural complexity, and fish community composition around Isla Solarte. The dataset is publicly available through Zenodo and accompanied by metadata and R scripts. This work demonstrates how structured citizen science programs can contribute locally relevant reef-monitoring data while also highlighting the need for continued training, quality control, and cautious interpretation of observer-generated datasets.
The Tropical Eastern Pacific Marine Conservation Corridor (CMAR) was established in 2004 through the cooperation of Colombia, Costa Rica, Ecuador, and Panama with the objective of safeguarding the migratory routes of large pelagic species such as sharks, rays, turtles, and marine mammals. As climate change modifies marine ecosystems worldwide, CMAR's recent ambitious conservation efforts might be affected by climate-driven species range shifts towards the Humboldt current. Here, we aim to identify possible adaptation and management strategies to enhance the climate resilience of biodiversity and fisheries in ten marine protected areas (MPA) of the CMAR region. We rely on scenario building and spatially-explicit integrated climate-fish-fisheries models to project the impacts of climate change on marine biomass of key marine species under different fisheries management and marine protection scenarios. Our results show that biomass in the CMAR region, and the effectiveness of MPAs in supporting biomass conservation, seafood production and sustainable tourism, are strongly impacted by higher-emission scenarios. Improving fisheries management and conservation could offset some of the impacts of climate change, especially if these are done in parallel. Adapting fisheries and MPA management plans within the CMAR region to climate-driven range shifts is essential to achieve their established conservation objectives. Improving our understanding of climate change impacts on marine biodiversity and biomass of key species of commercial importance can enhance the effectiveness of conservation and fishery management plans in building climate resilience of ecosystems in the region.
Symbioses between anemonefish and anemones are iconic images of tropical coral reefs, and important natural resources for tourism. It is critical to quantify anemones and their communities to help better protect these natural resources. This study examined the community structure of host anemones and surrounding associated organisms in two contrasting coral reef ecosystems in central Viet Nam. Via scuba-based ecological surveys, we examined communities in a comparatively disturbed reef area, Nha Trang Bay (NTB), suffering from poor water quality, destructive fishing, coral bleaching, and Crown-of-Thorns starfish outbreaks, and at a comparatively pristine reef in nearby Van Phong Bay (VPB). Seven species of host anemones and four species of anemonefish were observed across both bays. Anemones in VPB were observed to exist in shallower waters than in NTB, and to be larger in size. Immature damselfish D. trimaculatus, inhabited anemone species and coexisted with Amphiprion spp. We observed six additional species of fish that likely used host anemones as temporary shelters, and two cleaning fish species of wrasse (Labridae) that also coexisted with anemonefish. We also confirmed the presence of three species of cleaner shrimps and one species of anemone crab. There were distinct patterns of anemone-fauna associations with organisms tending to prefer specific host anemone species. For both host anemones and anemonefish, β-diversity in NTB was higher and had a more nested structure than that of VPB. However, β-diversity and its nestedness were observed to be reduced or comparable between the two regions after excluding study sites influenced by fishing and tourism. Until now, research on anemones has almost completely focused on hosts and anemonefish, but our data also show much is to be learned from associated invertebrate fauna as well, and future anemone studies would benefit from including such data. Overall, our results show differences in the depth distribution, host anemone sizes, diversity patterns, and associated communities of host anemones between NTB and VPB. Multivariate analyses indicated that associated community composition showed weak bay-level differences but clearer site-level structure, suggesting that local habitat conditions, disturbance histories, and host-anemone composition could be more important than general bay identity alone. These patterns are consistent with previously documented differences in reef conditions between the bays, although unbalanced site-level replication and limited site-level environmental data mean that causes of such differences need to be cautiously interpreted.
Abstract Genetic differentiation plays a key role in the resilience of reef-building corals under increasing environmental stress. In marine systems, patterns of genetic structure are often shaped by geographic distance and environmental heterogeneity, commonly described as isolation by distance (IBD) and isolation by environment (IBE). Here, we examined patterns of mitochondrial genetic differentiation in the brooding coral Porites panamensis across a marine protected area (MPA) and surrounding reefs in the southern Gulf of California. Using multivariate multiple regression on distance matrices (MMRR), we evaluated the relative effects of along-water geographic distance and environmental differences among sites. At fine spatial scales (≤ 20 km), environmental variation, quantified as Bray–Curtis dissimilarity in benthic community composition, was a significant predictor of genetic differentiation (β_env = 0.100, p = 0.018), whereas geographic distance was not. In contrast, at broader spatial scales (≤ 50 km), genetic differentiation increased with along-water geographic distance (β_geo = 0.0032, p = 0.015), consistent with isolation by distance. These results reveal a scale-dependent pattern of genetic structure, with environmental variation associated with genetic differentiation at finer spatial scales and geographic distance becoming more important at broader scales. Because this study is based on a single mitochondrial marker, the observed patterns reflect mitochondrial lineage differentiation and should be interpreted cautiously with respect to contemporary gene flow. Overall, our findings highlight the importance of spatial scale and environmental heterogeneity in structuring genetic variation within marine protected areas.
Andharmanik river is considered a fish refuge due to its unique habitat features, a natural mix of upstream freshwater and tidal exchanges with the Bay of Bengal. But the river is being polluted mostly by anthropogenic sources. The objectives of this study to highlight the first comprehensive effort to quantify heavy metal contamination in sediments, water and crab using ICP-MS, along with the associate health risk evaluation. Eleven metals named As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Se and Zn were assessed. Considering seasonal variations, the result showed that As, Co, Cr, Cu, Mn, Ni and Zn contents exceeded the recommended value in sediment. But, heavy metals content in water samples didn’t exceed the recommended value. In crab samples, metals like As, Cd, Cr, Cu, Fe, Pb and Zn had higher concentration than the recommended value. Among the two seasons, winter showed comparatively higher concentration (P < 0.05) for all samples studied except some cases. Meanwhile, the result of Risk Index (RI) indicated that sediment and water have no ecological risk. In crab, the value of total target hazard quotient (TTHQ) was higher than the acceptable limit of 1 depicting that the consumption of crab poses a carcinogenic risk for child and adult’s groups. Further, the Carcinogenic Risk (CR) value of Cr and Pb exceeded the threshold limit and suggested that there might be a significant health concern with prolonged exposure of contaminated crab for child ages. The findings indicated that the river ecosystem is contaminated by effluents from anthropogenic activities which need to be monitored to enforce environmental laws strictly for sustainable management.
Trace metal contamination in marine ecosystems poses risks to both ecological integrity and human health, yet baseline data from remote oceanic regions remain limited. This study presents the first comprehensive multi-tissue assessment of trace metal bioaccumulation in commercially important marine fishes from the Andaman Islands, India. Concentrations of eleven trace elements (Al, Cd, Cr, Co, Cu, Fe, Pb, Mn, Hg, Ni and Zn) were quantified in gills, liver, intestine and muscle of five fish species (Cephalopholis sonnerati, Epinephelus bleekeri, Auxis rochei, Rastrelliger kanagurta and Nemipterus japonicus) collected from major landing centres in South Andaman. Eight metals were consistently detected, while Hg, Cr and Co remained below detection limits across all tissues. Metal accumulation was strongly organ-specific, with liver acting as the primary reservoir for Cu, Fe and Cd, gills reflecting waterborne exposure to Mn and Al, and muscle exhibiting the lowest concentrations. Interspecies variation was limited, indicating broadly similar exposure pathways across trophic groups. Multivariate analyses confirmed clear separation of samples by tissue type rather than species identity. Human health risk assessment based on muscle tissue revealed Estimated Daily Intake and non-carcinogenic risk (HI < 1) values within acceptable limits for all species. However, Total Carcinogenic Risk values for Cd and Pb exceeded the USEPA benchmark, highlighting potential long-term risks for high-frequency consumers. Overall, the Andaman region exhibits a transitional contamination profile dominated by natural lithogenic inputs with emerging anthropogenic signals, underscoring the need for proactive multi-tissue monitoring and context-specific seafood risk communication.
The northern Bay of Bengal (NBoB) is one of the most underexplored and data-scarce regions of the global ocean, where strong freshwater input, monsoonal winds, and seasonal forcing interact to shape shallow upper-ocean structures. In this study, CTD profiles (collected in February and March in 2020) and gridded Argo data were combined with model output to evaluate mixed-layer depth (MLD), thermal inversion (TI), and differences between model and in situ observations across the coastal–offshore continuum. Coastal observations revealed extremely shallow mixed layers (4–12 m), strong haline stratification, and frequent wintertime temperature inversions that were often absent or muted in the model. Station-wise comparison showed a significant mismatch between CTD and model estimates, where the model generally overestimates MLD and smooths out fine-scale features such as abrupt temperature changes and multi-layer inversions. Offshore profiles highlighted strong near-surface stratification and well-developed thermocline structures that the model reproduced only below 80–100 m, and collocated Argo–model analyses showed warm, fresh, and low-density biases in the upper 50 m. These discrepancies likely reflect the combined effects of strong regional stratification, model vertical resolution, and limitations in representing fine-scale shelf processes. The results emphasize that continuous and expanded in situ observations remain important for characterizing subsurface structures and for improving evaluation of regional reanalysis products in the highly dynamic NBoB.
The increasing global use of rare earth elements (REEs) in high-technology industries has raised concerns about their release, persistence, and accumulation in marine environments. Although REEs were historically considered to exhibit relatively low toxicity, emerging evidence indicates that REEs act as ecological stressors, particularly for marine invertebrates that play fundamental roles in the structure and functioning of coastal ecosystems. This review synthesizes current knowledge regarding the occurrence, environmental distribution, and biological effects of REEs across major marine invertebrate groups, including mollusks, arthropods, and echinoderms. Reported effects include oxidative stress, altered enzymatic activity, impaired development and calcification, disturbed ion homeostasis, behavioral alterations, and trophic transfer. Mechanistic pathways are further examined, with an emphasis on cellular uptake, reactive oxygen species generation, membrane destabilization, and interference with calcium- and magnesium-dependent physiological processes. Building on this ecological risk perspective, the review also evaluates the mitigation potential of brown macroalgae, whose alginate- and fucoidan-rich cell walls exhibit strong binding affinity for REEs through biosorption. Evidence indicates that dried or processed macroalgal biomass can efficiently remove both light and heavy REEs from seawater, offering a nature-based strategy to reduce REE exposure in vulnerable marine invertebrate communities. A conceptual framework is proposed that integrates macroalgal biosorption with environmental monitoring, risk assessment, and coastal management. Key research gaps include defining chronic toxicity thresholds, identifying synergistic interactions with co-occurring pollutants, understanding long-term ecosystem consequences, and evaluating the scalability of biosorption systems under realistic field conditions. Overall, REEs represent a growing concern to marine biodiversity, while brown macroalgae represent a promising and nature-based approach for mitigation.
Heterotrophic diazotrophic bacteria (HDB) are increasingly recognized as widespread and significant contributors to oceanic nitrogen fixation. Macroalgae are known to form stable associations with endophytic and epiphytic bacteria for their growth, development and defense. The red alga Kappaphycus alvarezii can grow under nutrient-limited conditions, suggesting that nutritionally beneficial microbial associations may help sustain its growth under these conditions. The present study investigated the presence of HDB associated with K. alvarezii by incubating surface sterilized thallus sections in nitrogen-limited media. The isolates were taxonomically identified using 16S rRNA gene analysis, and their diazotrophic potential was assessed by amplifying the nifH gene. Phylogenetic analysis revealed associations with diverse genera, including Yangia, Salipiger, Mangrovicoccus, Tritonibacter, Pseudooceanicola, Roseibium, Thalassospira, Oceanobacillus, Alteromonas, Marinobacter, Pseudomonas, Stutzerimonas and Tenacibaculum. Eleven percent of the isolates, including Salipiger sp., Yangia sp., Thalassospira sp. Mangrovicoccus ximenensis and Stutzerimonas stutzeri tested positive for the presence of nifH gene, indicating potential diazotrophic capability. Our findings indicate that K. alvarezii hosts a diverse assemblage of culturable bacteria with potential host-beneficial functions, highlighting the need for functional validation of their contributions to the nitrogen acquisition and fitness of K. alvarezii.
