Seaweed farming is widely advocated as a nature-based blue carbon solution, yet its long-term impact on sedimentary carbon burial remains poorly constrained. Here, we assess this effect in a high-density Porphyra yezoensis farming area in Haizhou Bay, China, by analyzing surface and core sediments from farming (FA) and non-farming (NFA) sites for total organic carbon (TOC), inorganic carbon (TIC), total nitrogen (TN), stable isotopes (δ13C and δ15N), and their relationships. TOC and TN were slightly elevated in FA surface sediments relative to NFA, whereas TIC exhibited the opposite pattern, suggesting short-term organic enrichment. In contrast, sediment cores revealed no significant FA-NFA differences in TOC, TIC, or TN, indicating that the enrichment signal does not translate into long-term carbon burial. δ13C indicated that sedimentary TOC was primarily of marine origin. Estimated carbon burial fluxes were similar between FA (TOC: 7.2 ± 1.6 g m-2 yr-1, TIC: 17.7 ± 3.5 g m-2 yr-1) and NFA (TOC: 7.0 ± 1.5 g m-2 yr-1, TIC: 16.7 ± 3.4 g m-2 yr-1). Mechanistically, Porphyra farming suppresses phytoplankton growth via nutrient competition, reducing phytoplankton-derived carbon input. Moreover, Porphyra debris is highly labile and may potentially trigger decomposition of native recalcitrant organic carbon through a priming effect, limiting long-term burial efficiency. Our findings demonstrate no significant long-term enhancement of sedimentary carbon burial by intensive Porphyra farming. Although the activity may confer blue-carbon benefits, the assumption that seaweed farming augments sedimentary carbon sinks should be evaluated on a case-by-case basis rather than generalized.
Salinity fluctuations impose physiological challenges on estuarine organisms, but immediate behavioral responses may also depend on available habitat options. We characterized adult male Hemigrapsus crenulatus during the first minutes following transfer from 32 PSU to 6, 16, or 32 PSU. In Experiment 1, crabs had simultaneous access to sand and a submerged rock cavity for 720 s. In Experiment 2, the bottom was covered by either sand or shell hash, without a structural refuge, and crabs were observed for 300 s. Because each condition was represented by a single aquarium, observations, descriptive summaries, and principal coordinates analyses characterized individual patterns rather than independent treatment effects. In Experiment 1, 14 of 18 crabs entered the rock cavity: five of six at 6 PSU, five of six at 16 PSU, and four of six at 32 PSU. Refuge use, substrate occupation, refuge-entry latency, and behavioral transitions varied among individuals. In Experiment 2, completed burrowing occurred only in three of six crabs in shell hash at 16 PSU and was absent from the other salinity × substrate conditions. Median observed burrowing latency among these three crabs was 53.5 s (range 22.0-70.5 s). Wall-associated and wall-climbing events were common across the conditions examined. These findings show that H. crenulatus expressed multiple immediate responses following experimental transfer. Structural shelter was frequently used when available, whereas completed burrowing was uncommon without an alternative refuge. These exploratory patterns highlight the importance of habitat configuration and physiological timescale when examining behavioral responses to salinity variability.
Worldwide, grazing by sea urchins can create barrens habitat devoid of foliose macroalgae. Climate change has enabled urchins to poleward range extend, colonizing rocky reefs and reducing macroalgal forests. Tripneustes australiae, typically a vagrant on rocky reefs in southeast Australia where Centrostephanus rodgersii dominates, now appears at high densities. In 2024, many small T. australiae (<5 mm test diameter, TD) were reported within established C. rodgersii habitats along the coast of New South Wales. We investigated populations of T. australiae at 9 sites in this region in 2025 and 2026. To investigate species distributions relative to foliose macroalgal cover surveys were conducted to 20 m depth. We also assessed T. australiae size, recording the test diameter of 443 individuals across sites. Generalised Linear Mixed Models (GLMMs) showed that T. australiae abundance was positively correlated with macroalgal cover while C. rodgersii was negatively correlated. In one location T. australiae were predicted to be more abundant at depth, while C. rodgersii were always abundant in the shallows. Most T. australiae were large (>90 mm TD) indicating established adult populations. Information on these species where they co-occur with C. rodgersii is scant, and our results suggest synergistic grazing impacts. In contrast to C. rodgersii, grazing by T. australiae is not limited by depth or time of day. Aggregations of T. australiae at its southernmost range limit is a new phenomenon, suggesting a potential range extension front. As T. australiae prevalence increases, deep water may provide less refuge for macroalgae going forward.
As seaweed aquaculture expands globally, nitrogen (N) availability is becoming central to understanding both crop productivity and the biogeochemical role of coastal farming systems. Yet how bacterial assemblages and predicted N-transformation potential vary across cultivation phases remains poorly constrained. Here, we examined how environmental conditions and bacterial N-cycling potential varied across a Pyropia cultivation cycle on the central west coast of Korea. Early cultivation occurred under stronger freshwater influence and relatively high dissolved inorganic nitrogen (DIN) availability, with bacterial assemblages including taxa associated with particle-rich and surface-associated habitats. Mid-cultivation was marked by sharp DIN and dissolved organic carbon depletion, maximum dissolved N2O, reduced bacterial diversity, and a shift toward heterotrophic lineages associated with algal-derived organic matter. Tax4Fun2 profiles indicated lower predicted N2 fixation and nitrification potentials during this phase, but higher predicted ammonification potential and greater predicted abundance of downstream NO2- reduction biomarkers, including denitrification- and DNRA-related markers. After cultivation, partial DIN recovery coincided with a distinct bacterial assemblage and continued reconfiguration of predicted N-cycling biomarker profiles. These stage-resolved patterns suggest that nutrient depletion during cultivation was associated with shifts in the predicted potential for different N pathways, rather than demonstrating direct redistribution of N fluxes. Although direct rate measurements and functional gene validation are needed, our results identify mid-cultivation as a key biogeochemical window in which nutrient depletion, elevated N2O, bacterial assemblage reorganization, and predicted N cycle reconfiguration converge in a shallow Pyropia farming system.
Microplastics (MPs) are well-recognized as vectors for microbial colonization, forming complex biofilms known as the plastisphere. In this study, we investigated the colonization of four common plastic polymers, namely Linear Low Density Polyethylene (LLDPE), Polyethylene Terephthalate (PET), Polystyrene (PS), and Polyvinyl Chloride (PVC) with an average size range of 3.2-4.1 mm by marine microorganisms under natural shallow coastal water column conditions (∼2 m depth) near the fishing port of Gabès, in southeastern Tunisia (Gulf of Gabès, southern Mediterranean Sea). Biofilms were monitored over 7, 30, and 90 days using 16S rRNA gene amplicon sequencing to assess the simultaneous effect of exposure time and polymer type. Temporal succession emerged as the dominant driver of plastisphere composition, with PERMANOVA revealing that exposure time explained 58% of the total community variance (p = 0.001), while polymer type accounted for 15% (p = 0.001). Distance-based redundancy analysis (db-RDA) further demonstrated that this successional trajectory was closely associated with seasonal environmental shifts. Proteobacteria, Campylobacterota, Bacteroidota, and Actinobacteriota dominated the plastisphere, with Rhodobacteraceae, Saprospiraceae, and Flavobacteriaceae consistently established throughout. Putative hydrocarbonoclastic and plastic-associated taxa were detected at different stages of biofilm development, alongside organisms promoting biofilm cohesion. PET supported the most diverse biofilm, harboring approximately 2400 ASVs, including nearly 900 unique ASVs, after three months of exposure, whereas PVC hosted the most distinct microbial communities.
Few manipulative field studies have investigated lagoon ecosystem responses to climate-driven environmental stressors. To address these knowledge gaps, we investigated the response of structural and functional variables in the mercury-contaminated Grado Lagoon (northern Adriatic Sea) to water stagnation, i.e., a realistic condition potentially expected in the near future. To induce water stagnation, in June 2024 we positioned 18 mesocosms (∼0.8 m3 each), in the most contaminated and confined lagoon area, and compared the results with natural external conditions. The short-term (T1, 4 days) and long-term (T2, 10 days) isolation-driven effects on the ecosystem functioning were assessed by simultaneously investigating physical-chemical features of water and sediments, pelagic and benthic microbial communities’ biomass and structure, and the main biological processes. Water stagnation mimicked increased residence time in confined lagoon areas during summer and progressively triggered cascading effects, including oxygen reduction (T1, −52.9±7.4%), reduced primary production (T2, -64.6±18.0%), and dominance of all heterotrophic processes, compared to external autotrophic conditions. Our results show that even short-term stagnation and moderate oxygen reduction can trigger significant cascading effects on biological and biogeochemical processes, altering benthic-pelagic coupling. The rapid biomass increase of the microphytobenthic community under early stress conditions (T1, +86.5±42.2% vs outside), likely enhanced ecosystem resistance. Although hypoxic conditions were not reached, our results obtained in a single confined lagoon area/season, indicate that water stagnation significantly altered ecosystem functioning, suggesting that such conditions might be precursors to disrupting effects on the ecosystem and, if persistent or recurrent, could lead to dystrophic events in early summer.
Mangroves provide vital coastal ecosystem services, including shoreline protection, fisheries support, biodiversity conservation, and blue carbon sequestration. Using multi-temporal remote sensing and shoreline change analysis from 2015 to 2024, this study evaluates mangrove dynamics in the environmental influence zone of the Kyaukpyu Special Economic Zone and Deep-Sea Port, Myanmar. Mangrove area declined from 15,427.9 ha to 12,754.8 ha, representing a net loss of 17.3% and an average decrease of 253.3 ha/yr. Within the 3-km direct-impact Core Area (CA), mangrove cover contracted from 953.9 ha to 599.9 ha (37% loss; 39.1 ha/yr). Net change shifted from slight gain during 2015-2018 to loss-dominated dynamics during 2018-2021 and accelerated decline during 2021-2024. Shoreline analysis showed weak net erosion along both riverbanks, with erosion dominating the Yanbye Island margin and comparatively more coherent accretion along Made Island. Mangrove loss was concentrated within persistent and newly established embankment landscapes, consistent with land conversion and hydrological modification as important pathways of decline. Early gains included localized recolonization, some of which persisted into the following interval, but gains became progressively smaller and more fragmented. Hydrometeorological disturbances and governance constraints provided additional context but were not isolated as independent drivers. This study establishes a quantitative baseline for future monitoring and impact assessment under ongoing coastal development.
Per- and polyfluoroalkyl substances (PFAS) are persistent contaminants with pronounced surface activity and partitioning between water and particles, and habitat heterogeneity regulates their transport, redistribution and biological exposure within estuarine and coastal wetlands. This review synthesizes multimodal evidence from field surveys of water, particles, sediments, and biota, together with mechanistic studies of PFAS partitioning, transport, and biological responses. The resulting habitat-based framework links habitat heterogeneity to PFAS partitioning, transport, biological exposure, and food-web transfer, and relates these processes to consequences for biogeochemical cycling, biodiversity, and ecosystem services. Focusing on mangroves, salt marshes, and tidal flats, the study compares how hydrodynamic and salinity gradients, together with particle and sediment properties including organic carbon, clay, and transparent exopolymer particles, mediate PFAS retention and shape spatial exposure baselines for benthic organisms. Bioengineering effects, nursery-ground dynamics, and species habitat use can modify trophic exposure pathways, while reported food-web outcomes vary among systems, with trophic magnification observed for some long-chain PFAS and apparent biodilution reported in others. Building on these findings, habitat specific guidance is proposed for integrated management and risk assessment, emphasizing source reduction, explicit inclusion of the sediment phase, and PFAS multi-media evaluation supported by passive and non-target screening and bioaccumulation metrics interpreted in the context of life history and habitat use.
In gut-associated symbiosis, microbes play a pivotal role in shaping the habitat and diet preferences of the host. In intertidal deposit-feeding polychaetes, gut microbial assemblages are influenced by both water and sediment biota. In the present study, the metabolic profiling of gut microbial communities of Perinereis sp. was compared with its surrounding environmental microbiome. Effective utilization of amine, amino acids, and carbohydrate substrates by gut microbes was noticed within 48 h of incubation. Moreover, it reached an average well colour development of 0.54 at 120th hour of incubation. Low Gini coefficient (0.332) revealed a substrate-generalized communities with diverse metabolism pathways persist in the gut. The multi-level pattern analysis indicated some important substrates that were commonly utilized by gut as well as sediment microbes. Similarity percentage revealed maximum resemblance (64.1%) of gut microbes with its sediment which possibly explained by their deposit-feeding trait and diet preferences. Further, a generalized additive model was applied to study the non-linear trend in time-dependent utilization of carbon guilds by different microbial communities. The results overall indicate the functional overlaps in utilization pattern and possibly explain how polychaete gut microbiome share functional similarity with environmental microbiome with maintaining a distinct community structure. The capacity of utilizing wide varieties of substrate denote high metabolic plasticity of gut microbes which may help in host's survival in the organically enriched mudflat. Furthermore, overlaps in substrate utilization reveal that common environmental factors drive the ecological similarity between gut and sediment microbes.
Black carbon (BC) is a highly condensed carbon-rich substance mainly derived from incomplete combustion of fossil fuels, biomass, and other carbonaceous materials. Atmospheric BC is ubiquitous with strong light absorption capacity and long-range transport potential. With increasing anthropogenic emissions and climate-driven perturbations, its deposition into marine systems exerts profound impacts on regional biogeochemical cycles, yet large uncertainties remain regarding its aquatic ingress pathways, fraction-dependent transformation dynamics and long-term carbon sequestration potential. This review systematically synthesizes recent advances in the composition continuum, global distribution, and cross-sphere transport of atmospheric BC, as well as its subsequent transformation and fate following deposition into marine environments. Evidence indicates that BC is not a chemically inert pool, but a heterogeneous assemblage of fractions with distinct sources, structures, solubilities, and reactivities, whose fraction-dependent properties govern divergent environmental behaviors in marine systems. We clarify key drivers behind the uncertainties in BC flux estimates, elaborate divergent geochemical behaviors of heterogeneous BC fractions governed by physicochemical and biological reactions in the water column, and illustrate how refractory BC moieties are selectively preserved to sustain marine carbon sequestration. This work fills major knowledge gaps concerning the aquatic geochemical evolution of deposited atmospheric BC, advances the understanding of BC cycling across global and regional scales, and provides a theoretical foundation for evaluating the oceanic carbon sink potential of atmospherically derived BC. Future research should prioritize standardized BC characterization protocols, refined flux and biogeochemical process constraints, and integration of dynamic dissolved and particulate BC cycling into mainstream marine carbon budget models to ultimately quantify the carbon sequestration potential of atmospherically deposited BC.
Characterizing anthropogenic noise pollution in aquatic environments is inherently complex due to the multifaceted physical properties of acoustic waves, including variations in sound intensity, frequency, wavelength and temporal pattern. Among these parameters, contribution of specific frequencies, which are an integral component of broader noise spectrum remains poorly understood. To isolate the influence of this specific variable from overall complexity of underwater sound exposure, the present study employed Danio rerio as a model for aquatic developmental health and systematically investigated the effects of three distinct acoustic frequencies on early embryonic development. Different groups of fertilized eggs were exposed to either 40 Hz, 174 Hz or 528 Hz frequencies for 90 min daily, from 0 to 10 days post-fertilization, inside a soundproof acoustic box. Exposure to the low frequency sound waves i.e. 40 Hz, induced several statistically significant detrimental effects, like increased mortality, morphological abnormalities such as tail kinks, pericardial and yolk-sac edema, skeletal defects, histopathological changes in heart and eye regions, stunted growth, elevated oxidative stress and apoptosis. In contrast, 174 Hz frequency appeared largely benign, with no significant adverse effects observed across all developmental, morphological and physiological parameters. The 528 Hz frequency did not cause overt morphological damage, mortality or significant apoptosis. However, it induced a modest increase in GST activity. Overall, these findings identify low frequency sound as discrete drivers of noise-induced stress and provide critical evidence for environmental risk assessment. Also, the study highlights the need for further investigation of frequency-specific safety thresholds for vulnerable early-stage aquatic organisms.
The increased routine use of marine gas oils (MGO) has increased the risk of marine oil spills during its transport, use and disposal, threatening open ocean and coastal environments. One of the standard oil spill remediation methods is the application of chemical dispersants to break down surface oil slicks. Although previous studies have investigated the toxicity of MGO through its water accommodated fractions (WAF), few have examined how chemically enhanced WAF (CE-WAF) produced by the application of commercial dispersants, modifies the toxicity to marine organisms in cold environments. The copepod Calanus finmarchicus is an important component of the zooplankton community of the North Atlantic and an important dietary source of food for several commercially important fish species. C. finmarchicus has been extensively used in studies concerning hydrocarbon contamination, thus making it a suitable organism to investigate relevant environmental effects of the CE-WAF from MGO. Hence, the objective of this study was to investigate relevant sublethal effects of an MGO treated with the dispersant FinaSol OSR52 (10% of oil mass) on the defensome of C. finmarchicus. Adult C. finmarchicus were exposed under static conditions for 24, 48, 72 and 96 h to a sublethal concentration of CE-WAF corresponding to half of the calculated acute LC50-value after 96 h. Sublethal effects were investigated by observing the transcription patterns of selected biomarker genes, activities of oxidative stress biomarker enzymes, levels of lipid peroxidation, and accumulation of the carotenoid astaxanthin in its free form. Gene transcription analysis showed significant downregulation of the biotransformation gene cyp 330A1 in all the exposed groups compared to controls, and changes in the transcription levels of genes such as elongase, fatty acid binding protein and ferritinThis suggest that exposure to CE-WAF affected lipid metabolism and consequently affected the ability of the copepods to store energy. A significant reduction in activities of the oxidative stress biomarker enzymes, such as Catalase, Superoxide dismutase and total Glutathione, suggests that exposure to the CE-WAF induced oxidative stress, likely through depletion or inhibition of the antioxidant defense system. However, no significant difference was observed among exposure and control groups regarding lipid peroxidation. Finally, the 24 h exposure affected the concentrations of the carotenoid astaxanthin in free form, suggesting that exposure affected the dynamics of the utilization of astaxanthin in the copepod.
