Algal biomass, comprising primarily proteins, carbohydrates, and ash, serves as a high-quality precursor for functional carbocatalysts, with each component significantly influencing the catalytic properties. This study investigates the effects of selectively removing these components from carbocatalyst precursors on the structural and chemical properties of the resulting carbocatalysts and their catalytic performance in the pyrolysis of alkali lignin. Results show that the removal of any component increased the micropore area fraction of the carbocatalyst. Specifically, the removal of proteins and carbohydrates led to higher pyridinic N content, which suppressed ketone formation and enhanced aldehyde production during pyrolysis. Ash removal considerably reduced the specific surface area of the carbocatalyst but promoted the formation of pyrrolic N and graphitic N, increasing the yield of phenols from 59.85% to 66.21%. Based on the product distribution, a reaction pathway was proposed to elucidate how the carbocatalysts affect the volatile behavior of lignin during pyrolysis. This study provides a valuable reference for the targeted design of biochar catalysts and the high-value utilization of lignin resources.

Environmental DNA (eDNA) metabarcoding provides a non-invasive tool for monitoring marine biodiversity in complex ecosystems. In this study, we applied eDNA techniques to investigate the spatiotemporal dynamics of fish communities in Daya Bay, South China Sea, by analyzing 120 water column and 113 sediment samples collected across four seasons. Our research aimed to characterize the seasonal turnover and habitat-specific partitioning of fish community structures. The results revealed that sediment matrices exhibited significantly higher alpha diversity compared to water samples. However, sediment showed lower community heterogeneity-quantified as within-group Bray-Curtis dispersion-particularly during the warm seasons (spring and summer) compared with the water column. Conversely, during the cold seasons (autumn and winter), sediment matrices showed lower alpha diversity but higher community heterogeneity. Using LEfSe and random forest models, we identified a suite of discriminative indicator taxa that characterized these community shifts. Based on relative read abundance (RRA), Johnius and Pennahia were significantly enriched in the water column, while Cynoglossus and Zebrias were primarily associated with sediment habitats. These findings highlight the complementary roles of water and sediment eDNA in capturing the full spectrum of fish biodiversity. While this study primarily describes observed patterns within a dynamic hydrographic context, it provides foundational data for advancing eDNA-based biomonitoring in subtropical marine ecosystems and supports the development of targeted conservation strategies.

Anthropogenic activities in Daya Bay (DYB), a prominent aquaculture region and also a petrochemical industrial estate in Guangdong Province, China, may pose potential hazardous to environmental safety. The present study investigated the distribution of 16 polycyclic aromatic hydrocarbons (PAHs) listed by the USEPA (EPA 16 PAHs) and 18 alkylated PAHs (18 APAHs) in seawater and surface sediments of DYB in dry, wet, and normal seasons. The results indicated that the average concentrations of E34 PAHs in seawater ranged from 584.02 f 107.54-961.07 f 621.61 ng/L across different seasons, while the average concentrations of the EPA E16 PAHs in seawater varied between 265.63 f 55.66 and 424.16 f 267.55 ng/L. In surface sediments, the concentrations of E34 PAHs ranged from 350.52 f 33.33-571.33 f 98.76 ng/g, E16 PAHs from 185.21 f 34.24-270.04 f 55.78 ng/g, which were three orders of magnitude higher than in the aqueous phase. No significant seasonal variation was found in sediments PAHs. APAH accounted for a significant proportion of E34 PAHs. Low-and medium-molecular-weight PAHs were predominant in both seawater and sediments. Molecular ratios diagnose and PCA analysis suggested that the primary sources of PAHs in seawater were inputs from petroleum products and pyrolysis products related to transportation, the PAHs in sediments were mainly from fossil fuel combustion and diagenesis. Incremental lifetime cancer risk values suggested that the health risks associated with PAHs in DYB seawater were below USEPA risk levels. Compared with previous reports, the concentration of E16 PAHs in both seawater and surface sediments of DYB has shown a gradual decline over the past 20 years. The results of this study provided valuable insights into PAHs contamination and trends in marine environment protection within this region, which has undergone more than 30 years of rapid economic development.

Alga, rich in lipids and nitrogen, is a promising biofuel feedstock to alleviate the fossil fuel scarcity and reduce CO2 emission and thus is pyrolyzed to obtain bio-oil. To further reduce the content of heteroatoms (O and N) within bio-oil, catalyst was applied to the pyrolysis. Aiming at developing economical catalyst, this study takes algal char from pyrolysis of Sargassum fusiforme (SF) as the feedstock of nitrogen-doped carbon catalyst and evaluate the catalyst performance on SF pyrolysis. Specifically, several catalyst preparation parameters, such as chemical activation agents (NaOH and KOH), activation temperature (700-900 degrees C), the ratio of chemical activating agents (50 %-66.7 %) and activation atmosphere, were systematically considered. The obtained catalyst was evaluated and applied to catalyze the pyrolysis of SF. It was found that the optimized condition was 800 degrees C and 40 % load of NaOH and such activation enhances the catalyst's specific surface area, predominantly microporous structure and higher pyrrolic nitrogen and oxidized nitrogen. Especially, NaOH activation, rather than KOH activation, facilitates the incorporation of more pyrrolic nitrogen and oxidized nitrogen. With these beneficial properties, catalyst effectively facilitated the cracking and reformation of volatile compounds through decarboxylation, decarbonylation, dehydration, and aromatization reactions, resulting in an increase in hydrocarbons in the bio-oil to 27.79 % and a rise in non-condensable gases from 22.65 wt% to 28.67 %-33.05 wt%. With such findings, this study shows the feasible application of self-originating catalyst to catalytic pyrolysis.

Currently, many global coral reef ecosystems are experiencing varying degrees of habitat degradation, raising the possibility of changes in the trophic structure of coral reef fish. Understanding how these trophic structures change over time is crucial for explaining the adaptive capacity of organisms under different environmental pressures. This study employed stable carbon and nitrogen isotope techniques to investigate the trophic dynamics of 21 species of parrotfish coexisting in the coral reef area of the Xisha Islands, South China Sea from 2018 to 2024. Under the combined pressures of coral reef habitat degradation and human activities, parrotfishes exhibited significant isotopic shifts over the seven-year study period. These shifts were reflected in a progressive increase in both nitrogen (δ15N) and carbon (δ13C) stable isotope values of the community, a pattern consistent with a potential change in assimilated dietary resources. Concurrently, the isotopic niche breadth of the community narrowed, indicating a pattern of dietary specialization toward a subset of available food resources, a trend that aligns with predictions from optimal foraging theory. Additionally, the overlap in trophic niches among different feeding functional groups (Scrapers, Excavators, and Browsers) increased, leading to higher dietary similarity. Parrotfish populations showed a decline in dietary diversity and trophic redundancy, whereas the stability of the trophic structure increased, especially within the Browser group. These findings enhance our understanding of the feeding adaptation strategies of coral reef fish in changing environments and provide an important foundation for future monitoring and conservation efforts of coral reef ecosystems. They are essential for maintaining the ecological functions of coral reef fish and the health of the ecosystem.

The diversity of marine habitats influences fish trophic niches and adaptation strategies. This study investigated fish trophic niches in cold seep and adjacent areas of the South China Sea in August 2023 using stable isotope techniques. It examined these niches across different depths and compared trophic strategies between cold seep and non-cold seep habitats. The δ15N values of fish in the cold seep area increased with depth, indicating shifts in trophic levels, while the δ13C values increased solely in the cold seep area. Bayesian analysis revealed that deeper fish in the cold seep area preferred shrimp, whereas those in the control area leaned towards cephalopods. At depths exceeding 500 ​m, the trophic niche of the fish community in the cold seep area was broader than that in the control area, although the individual niches of shared species were narrower. This finding suggests a balance between resource diversity and individual feeding specialization within the cold seep fish community at greater depths. In contrast, individual niches in the control area expanded to adapt to a resource-limited environment. Additionally, the overlap of trophic niches between deep-sea and shallow-water fish diminishes with increasing depth in both regions. We hypothesize that beyond a certain depth, mesopelagic fish either cease vertical migration or modify their patterns of vertical migration. These results underscore the essential role of cold seep ecosystems in sustaining deep-sea biodiversity and intricate trophic structures, thereby enhancing our understanding of adaptive strategies in deep-sea fish communities.

Parrotfish are a key functional group in coral reef ecosystems, and their feeding behavior directly regulates the coral–algae competition balance and drives bioerosion processes. In this study, we aimed to elucidate the algal control mechanisms and sympatric coexistence strategies of parrotfish on coral reefs by resolving their detailed dietary composition. We analyzed 10 co-occurring parrotfish species from the Qilianyu Islands, Xisha Islands, using 18S and 16S rRNA high-throughput sequencing for DNA metabarcoding of intestinal contents, combined with complex network analysis to systematically examine dietary composition, trophic niche differentiation, and food web structure. The results showed that: (1) parrotfish have a broad dietary spectrum covering eukaryotic algae, prokaryotic algae, and benthic invertebrates; (2) significant dietary differentiation exists among functional groups, with Browser preferring coralline algae (21.30%), Excavator favoring microalgae (21.40%), and Scraper mainly consuming surface filamentous algae (18.28%); this differentiation alleviates interspecific competition through fine-scale resource partitioning; (3) the parrotfish–prey network exhibits significant modularity, with Phaeophyta, Chlorophyta, Platyhelminthes, Pyrrophyta, and Synechococcales (Cyanobacteria) serving as key nodes maintaining network stability. This study demonstrates that multi-level dietary differentiation is the core mechanism enabling sympatric coexistence of the 10 parrotfish species, and that complementary feeding strategies among functional groups facilitate comprehensive coverage of diverse algal types. These findings provide important scientific bases for the conservation and restoration of coral reef ecosystems.

Coastal lagoons are crucial transitional zones connecting land and sea, and their ecological connectivity with adjacent open waters directly sustains regional biodiversity and ecosystem functions. However, how lagoon fish communities connect on a diurnal timescale remains poorly understood. In this study, we selected Xincun Lagoon on the southeastern coast of Hainan Island, China, as the study area. We established six sampling stations along an environmental gradient from the lagoon interior, through the tidal inlet, to the open sea, and conducted repeated diurnal sampling at six time points on 24 January 2024. Using eDNA metabarcoding, we analyzed the spatiotemporal dynamics of fish communities to examine spatial functional differentiation within the lagoon ecosystem and the potential corridor role of the tidal inlet. Our results showed clear spatial functional differentiation of fish communities along the environmental gradient. The lagoon inlet (XC4) exhibited the highest rate of community temporal change and the greatest amplitude of diversity fluctuation, with a peak change rate of 0.854 during the evening period (18:00-21:00). Its coefficient of variation for Shannon diversity was 6.2 times that of the mangrove creek (XC3). The mangrove creek area (XC3) had the highest Shannon diversity and the smallest fluctuations, functioning as a biodiversity hotspot and a region of relatively stable community structure. Within the lagoon interior, the temporal dynamics at the marginal zone (XC1) were substantially stronger than those in the central zone (XC2). Offshore stations indicated that the ecological influence of the lagoon extended to the 5 m isobath but weakened at the 10 m isobath. Furthermore, Clupeidae eDNA signals were strongest inside the lagoon during the day, at the tidal inlet in the evening, and in offshore waters at night. This study demonstrates the utility of eDNA metabarcoding for capturing fine-scale diel variation in fish community composition and distribution across the lagoon-inlet-offshore gradient, providing information that is difficult to obtain through conventional surveys. These patterns suggest, rather than confirm, that the tidal inlet may play an important role as a corridor linking lagoon and offshore habitats, and provide a reference case for using eDNA technology to study fine-scale connectivity in similar systems.

Against the backdrop of addressing industrial carbon emissions, microalgae are recognized as a potential source of carbon-neutral biofuels. This study proposes a novel cascade cultivation strategy for Chlorella vulgaris, which integrates exogenous phytohormone application and semi-continuous operation. The strategy is implemented in three distinct phases, initial biomass accumulation, semi-continuous dilution, and lipid synthesis. Experimental results show that the combination of 25 mg L-1 indole-3 acetic acid (IAA) and 20 % CO2 significantly enhances biomass productivity, with biomass productivity reaching 0.234 g L-1 d-1, 1.73-fold higher than that of the control group without IAA addition under 20 % CO2. During the lipid synthesis phase, applying 30 mg L-1 abscisic acid (ABA) under 0 % CO2 conditions increases the lipid content to 33.1 %, which is 1.90-fold higher than that of the control. Additionally, the semi-continuous cultivation mode enhances the tolerance of micro-algae to high CO2 concentrations. The proposed phased strategy effectively promotes both CO2 fixation and lipid accumulation in C. vulgaris, demonstrating its potential for promoting the development of microalgae-based carbon reduction and biofuel production.

The Xisha coral reefs are highly biodiverse ecosystems in the South China Sea, China. Bacterial communities drive energy flow and biogeochemical cycling in coral-reef ecosystems, and serve as indicators of reef health. Yet the composition and dynamics of both bacterial assemblages and ARGs within the Xisha coral reefs remain poorly resolved. This study used 16S rRNA amplicon and metagenomic sequencing to compare bacterial community structure across surface and bottom waters, and surface-water ARGs profiles, in Beijiao Reef (BJ; an uninhabited reef) and Qilianyu Islands (QLY; an inhabited island) of the Xisha Islands. The results revealed bacterial community composition, bacterial co-occurrence network structure, and ARGs profiles differed markedly between the two reef areas. Dominant genera-Prochlorococcus_MIT9313, Salinimonas, Synechococcus_CC9902, Vibrio, and Alteromonas-were significantly more abundant in BJ (p < 0.05), whereas QLY showed higher abundances of Planococcus, Psychrobacter, Jeotgalibacillus, Salinicoccus, and Marinococcus (p < 0.05). The QLY bacterial co-occurrence network exhibited greater complexity (higher clustering coefficients and modularity), whereas the BJ network was simpler but displayed significantly higher closeness-centrality values (p < 0.001). Surface waters of the Xisha Islands were dominated by tetracycline, aminoglycoside, and macrolide resistance genes, whereas sulfonamide and multidrug resistance genes were less abundant. In addition, ARGs concentrations in BJ were slightly higher than those in QLY, suggesting that human habitation may not be a key environmental factor influencing ARGs concentrations in the seawater of the Xisha Islands. Correlation analysis showed that high-abundance ARGs in BJ (msbA, RanA, tetB(P), tet(T)) were linked to phototrophic Prochlorococcus_MIT9313 and Synechococcus_CC9902, whereas QLY dominant ARGs (baeS, patB, MexW) correlated with Gram-negative Vibrio and Pseudomonas. These ARGs are involved in bacterial efflux mechanisms, reflecting adaptive responses to environmental stress. This study provides valuable insights for assessing water quality and evaluating the impacts of human habitation pressure on coral reef ecosystems in the Xisha Islands.

The adaptive strategies of species to differentiated habitats represent a universal ecological principle. This study takes Chauliodus sloani, a dominant mesopelagic fish in cold seep-adjacent waters, as a model to explore the adaptive patterns of its trophic niche in differentiated habitats. In August 2023, C. sloani samples were collected at different depths (75-750 m) and regions (cold seep and non-cold seep areas). Stable carbon and nitrogen isotope techniques were employed to characterize their trophic niche attributes. Results indicated that the S13C value of C. sloani in cold seep-adjacent waters was-19.29 +/- 0.31 %o, S15N was 9.83 +/- 0.53 %o, and the trophic level was 3.37 +/- 0.68. Trophic indicators including carbon isotope range (CR), nitrogen isotope range (NR), mean centroid distance (CD), mean nearest neighbor distance (MNND), and standard deviation of MNND (SDNND) were higher in non-cold seep areas than in cold seep areas at the same water depth. This supports that C. sloani in cold seep areas exhibit lower dietary diversity but higher redundancy and evenness, endowing populations with stronger anti-disturbance capabilities. The directional changes in trophic structures further validated this result, confirming more stable trophic structures in cold seep populations. At 750 m depth, C. sloani exhibited minimal overlap in core trophic niche (SEAc) with other depths, demonstrating significant niche differentiation and independent population establishment at the strata. Zooplankton constituted the primary food source of C. sloani, but the contribution ratio of food sources varied significantly with depth. The contribution ratio of cephalopod prey increased with increasing water depth. This research elucidates both the adaptive strategies of C. sloani trophic niches across heterogeneous habitats and verifies distinctive diel vertical migration behaviors in mesopelagic fishes, offering novel insights into deep-sea organism survival mechanisms within complex ecosystems and associated energy transfer pathways.

Cold seeps, unique deep-sea ecosystems driven by hydrocarbon- and sulfide-rich fluid fluxes, support mesopelagic fish communities. Fish gut microbiota are vital to host metabolism and health, and interact closely with the surrounding water environment. However, information on gut bacterial composition and potential functional profiles of mesopelagic fishes in the cold seep has rarely been explored. In this study, high-throughput sequencing of the 16S rRNA gene was used to compare gut microbiota of mesopelagic fishes collected from the cold seep environment (Bolinichthys longipes, Ceratoscopelus warmingii) and mesopelagic fishes from non-cold seep environment (B. longipes, Diaphus brachycephalus, Diaphus signatus). Significant differences were found in gut bacterial composition and predicted functional profiles between the two distinct fish habitats. Within B. longipes, clear differences in gut bacterial composition were detected between cold seep and non-cold seep populations, suggesting a potential habitat-associated effect. The genera Blastopirellula, Ruegeria, and Rubripirellula, which are known to be involved in sulfide and hydrocarbon transformations, were significantly more abundant in cold seep fish (p < 0.05). In contrast, Acinetobacter was significantly enriched in fish outside the cold seep (p < 0.05). The differences in gut bacterial composition between the two habitats were primarily driven by the “abundant” subcommunities. Co-occurrence network analysis revealed more complex gut microbiome networks in cold seep fishes. Functional predictions using FAPROTAX showed that the gut microbiome associated with cold seep fish harbored higher predicted functional potential related to methane-, nitrogen-, and sulfur-associated processes. Meanwhile, PICRUSt2 analyses indicated a higher representation of predicted pathways associated with lipid metabolism and hydrocarbon degradation under cold seep conditions. Together, these results suggest that the cold seep environment may influence the structure and predicted functional potential of mesopelagic fish gut microbiota.

The spatiotemporal distributions of the phytoplankton community and harmful algal bloom (HAB) species were investigated in the northern South China Sea (SCS), central-western SCS, Nansha Islands, and Xisha Islands based on sized-fractionated chlorophyll a (Chl a), morphological identification (MI), and 18S rDNA high-throughput sequencing (HTS). The results revealed that phytoplankton in the SCS showed pelagic characteristics, with small-sized microalgae (<20 μm) dominating (>85% of total biomass). Specifically, picoplankton predominated during the spring transition period (ST period), whereas nano-sized microalgae prevailed during the southwest monsoon (SW period). A total of 309 phytoplankton species were identified via MI, 32 of which were recognized as HAB species based on the combined results of MI and HTS. Spatial factors primarily influenced phytoplankton abundance, whereas temporal dynamics governed community succession. Although total abundance showed no significant temporal variation, distinct shifts in community structure were observed: diatoms, cyanobacteria, and dinoflagellates accounted for 57.72%, 25.60%, and 16.18% of the average abundance, respectively, during the ST period, whereas diatom contribution increased to over 85% during the SW period. HAB species abundance was significantly higher in the SW period than in the ST period, with peak values primarily occurring around the Xisha Islands. HTS revealed significant differences in community structure between island-reef and offshore stations, as well as among different depth layers. Phytoplankton communities were mainly distributed above 75 m, with the highest concentration between 50 and 75 m. Redundancy analysis (RDA) indicated that temperature, salinity, and depth were the key environmental factors influencing the spatiotemporal distribution of phytoplankton communities in both offshore and island-reef regions of the SCS. This study provides the first comprehensive characterization of the vertical distribution patterns of phytoplankton in the pelagic regions of the SCS.

Habitat fragmentation is a major driver of biodiversity change in coastal systems. In planktonic ecosystems, ecological connectivity reflects the degree of biological exchange and community similarity between habitat patches, shaped conjointly by physical transport and ecological selection. Quantifying ecological connectivity thus provides a robust framework to evaluate the extent of habitat fragmentation and its ecological consequences in coastal systems. Based on integrated morphological observation and high-throughput sequencing (HTS), our study characterized the qualitative and quantitative composition of phytoplankton communities in Xincun Bay Lagoon (Hainan Island), with a specific focus on harmful algal bloom (HAB) species, to elucidate their biological connectivity between the semi-enclosed lagoon and the open ocean. The Venn diagram revealed that among the 4708 identified phytoplankton amplicon sequence variants (ASVs), 2094 (44.48%) were exclusively present in the lagoon versus the inlet, while 3268 (69.41%) were unique to the lagoon compared to the open sea. Furthermore, nonmetric multidimensional scaling (NMDS) confirmed significant differentiation between the lagoon and open-sea phytoplankton communities. SourceTracker analysis further indicated low compositional similarity between these areas, with a predicted contribution of 73.80% from the inlet to the lagoon ASVs, compared to a much lower contribution (22.60%) from open-sea sources. The mean abundance stood at 1.3 × 103 cells L−1, with peak concentrations observed in the lagoon station. Integrated morphological observation and HTS analyses identified 30 HAB species within the lagoon, including 10 toxin-producing taxa. Based on HTS, the abundance of HAB species in the lagoon was significantly higher than in the open sea (p < 0.05), while the Shannon-Wiener diversity index was significantly lower. Mantel tests and redundancy analysis (RDA) revealed phosphate concentration and water temperature may be important factors influencing the distribution of phytoplankton. This study underscores the urgent need to address habitat fragmentation in coastal lagoons and highlights how constrained ecological connectivity, coupled with localized nutrient enrichment, elevates the potential risk of HAB outbreaks.

Traditional zooplankton net sampling provides well-established approaches for species identification and density estimation; however, it is often subject to physical filtration, sample compression, and behavioral avoidance, which can lead to underestimation of small-sized or fragile taxa. Moreover, such methods have limited capacity to resolve fine-scale spatial distributions and aggregation patterns of zooplankton under in situ conditions. In recent years, underwater in situ imaging has emerged as a promising tool for zooplankton investigations owing to its ability to provide non-invasive, real-time observations in the natural environment. In this study, underwater in situ zooplankton imaging data collected during winter 2023 and spring 2024 in the Ningyuan River estuary, Hainan Island, were used to examine seasonal variations in community structure, niche differentiation, and environmental responses of zooplankton in this tropical estuary. The results revealed pronounced seasonal differences in zooplankton communities. Winter assemblages were characterized by higher overall abundance and were dominated by Chaetognatha and Copepods, whereas spring assemblages exhibited lower abundance but a more diverse taxonomic composition, with Copepods and tunicates as the dominant groups. Chaetognatha and Copepods displayed relatively broad niche breadths, while most other taxa exhibited intermediate to narrow niches. Niche overlap and variance-ratio results suggested that overall interspecific association was weak and non-significant in both seasons, with a slight segregation tendency in winter (VR = 0.76) and a slight co-occurrence tendency in spring (VR = 1.79). Multivariate analyses further indicated that water temperature, salinity, dissolved oxygen (DO), and pH were the primary environmental factors associated with the spatial patterns of zooplankton communities. These findings improve our understanding of zooplankton responses to environmental gradients in tropical estuarine systems and highlight the value of integrating in situ imaging into multi-source monitoring frameworks.

Global coral reef ecosystems face various levels of disturbance pressure. Understanding the depth-structured variation in coral reef fish communities can help us to better grasp and predict the adaptive changes of the ecosystem under different stressors. This study applied eDNA metabarcoding technology to analyze the spatial distribution of the coral reef fish at various depths (0 m, 5 m, 10 m, 15 m, 20 m, 30 m, 40 m, 50 m, and 60 m) within the Xisha Islands of China. The results indicated that the eDNA technology detected a total of 213 amplicon sequence variants (ASVs), including 33 species that were not identified using traditional methods. Herbivorous fish generally dominated in relative abundance across different depths. Moreover, the similarity among depth groups was largely absent, and significant differences existed in fish assemblages across depth gradients, consistent with the unique depth preferences of fish microhabitats. Importantly, our findings revealed distinct depth-structured variation among different functional groups of coral reef fish. Large carnivorous fish initially increased and then decreased along the depth gradient from 0 to 60 m, with a turning point around 20 m, while large herbivorous fish displayed the opposite trend. Small carnivorous and small herbivorous fish consistently declined along the same depth gradient. Additionally, the Margalef index (D) and Function richness (FRic) both displayed a consistent downward trend with increasing depth, while the Shannon–Wiener index (H′), Pielou index (J′), Quadratic entropy (RaoQ), Functional dispersion (FDis), and Functional evenness (FEve) initially increased and then decreased, peaking around 20 m. This study revealed that eDNA metabarcoding is an effective tool for evaluating coral reef fish biodiversity, community composition, and spatial distribution. It enhances our understanding of distribution dynamics and offers valuable insights for coral reef conservation and restoration efforts.

The diversity and spatial-temporal distribution of phytoplankton HAB species, contamination status of oyster toxin, and their sources were investigated in Jiangmen oyster farming area based on morphological observation and liquid chromatography-tandem mass spectrometry analysis. The results revealed there were 28 HAB species, including 19 harmless HAB species, two toxic species (Akashiwo sanguinea and Karenia brevis), and seven toxin- producing microalgae (Alexandrium pacificum, Dinophysis caudata, D. miles, D. fortii, Gonyaulax spinifera, Gymnodinium catenatum, and K. mikimotoi). The mean abundance of total HAB species generally showed a trend of increasing from winter to autumn. The total average abundances of toxic HAB species were 269, 265, 321 and 2.6 x 103 cells L- 1 in winter, spring, summer and autumn, respectively. Redundancy analysis showed temperature, dissolved oxygen, silicate and phosphate were the key factors related with variations of HAB species. Only spring oyster samples were detected paralytic shellfish toxins (PSTs) (1/15), and the composition included gonyautoxins (GTX1&2) and decarbamoyl gonyautoxin 2 (dcGTX2), with a total toxicity level of 9.96 mu g STXeq kg- 1. N-sulfocarbamyl (C1) and decarbamoyl gonyautoxin 3 (dcGTX3) were observed in the net-concentrated phytoplankton samples. It is inferred that these five types of PSTs derived from A. pacificum. The cultured oysters were observed five types of low-concentration lipophilic marine toxins (LMTs) including okadaic acid (OA), dinophysis-1 (DTX1), pectenotoxin-2 (PTX2), gymnodimine (GYM), and homo-yessotoxin (homo-YTX). Though the levels of PSTs and LMTs in the cultured oysters were low, the presence highlights a potential threat to the safety of oyster products from HAB species.

Habitat heterogeneity and human disturbances drive variations in interspecific interactions among fish species. Trophic niche analysis is a crucial approach for understanding these interactions. This study investigates the interspecific interaction mechanisms of two scorpionfish species, Sebastiscus marmoratus and Scorpaenopsis cirrosa, across different habitat conditions in the Wanshan Archipelago of the Pearl River Estuary. Three island groups-Guishan Island, Wailingding Island, and Dongao & Wanshan Islands-were selected as study sites. Using carbon and nitrogen stable isotope analysis, we examined variations in their trophic relationships. The results revealed significant regional differences in the δ13C values of S. marmoratus and S. cirrosa (p < 0.05), indicating regional variation in their food sources. Bayesian mixing model analysis showed that at Guishan Island, annelids constituted the primary food source for both species. However, at Wailingding Island and Dongao & Wanshan Islands, their reliance on annelids significantly decreased, with a preference shift towards mollusks, reflecting region-specific foraging strategies and niche differentiation. The δ15N values of the two species did not exhibit significant regional differences, suggesting that S. marmoratus and S. cirrosa occupy similar trophic levels across different regions. Trophic niche metrics, including CR, NR, CD, and TA, indicated that S. cirrosa has a broader trophic niche, suggesting a more flexible feeding strategy and a potential competitive advantage in resource utilization. The two species exhibited overlapping trophic niches, with distinct regional variations. Notably, at Guishan Island, where trophic niches were the broadest, potential competition between the species was most pronounced, which may be associated with higher human activity intensity. Differences in ecosystem structure among islands contributed to variations in food resource availability and niche space, ultimately shaping the foraging behaviors and adaptive strategies of S. marmoratus and S. cirrosa across regions. These findings provide theoretical insights into interspecific interactions in heterogeneous habitats and inform fisheries resource conservation.

Sediment cores were collected from the nearshore to bay mouth region in Daya Bay, aiming to describe the historical patterns of heavy metals deposition in the sediment. During the last 40 years, the heavy metals exhibited significant different deposition behaviors in the sediment, in which As, Zn, Cr were more enriched and contributed to metals pollution in this area. Moreover, heavy metals deposition exhibited completely opposite behaviors from the nearshore to bay mouth region. An increasing of pollution level and ecological risk was observed in the nearshore, whereas a decreasing trend was detected in the bay mouth. Principal component analysis suggested that heavy metals were possibly derived from anthropogenic activities in the nearshore, whereas natural sources were the main sources in bay mouth. The results indicated the urgency of implementing efficient measures to mitigate heavy metals contamination in the adjacent sea.

Meiji Reef, in the east-central Spratly Islands, is a typical coral reef ecosystem with high fish biodiversity. To investigate fish community dynamics, we integrated multiple survey methods (longlining, hand-lining, drift gillnetting, dive fishing, and eDNA) with historical records (1998-1999, 2004, 2012, 2016-2019) and field surveys (2020-2024). The objectives were to characterize community composition, reveal long-term changes from 1998 to 2024, and assess succession following island reclamation. This integrated dataset enabled a systematic analysis of evolutionary trends in fish community structure at Meiji Reef. As of 2024, a total of 353 coral reef fish species have been documented, classified into 162 genera, 61 families, and 14 orders. Small fishes (43.81 %) and carnivorous fishes (74.92 %) dominated the community. We found a marked decline in the number of large carnivorous fish species since the 1998-1999 surveys, alongside an increase in the proportion of small carnivorous fishes and an overall reduction in mean length and weight of carnivorous fishes. The similarity coefficients for carnivorous fish species across different periods were consistently low, categorized as either "very dissimilar" or "dissimilar," indicating substantial community turnover. However, during the 2020-2024 period, the proportions of large carnivorous fishes and reef-dependent taxa, such as the Serranidae family, notably increased compared to 2016-2019, whereas proportions of smaller carnivorous species and taxa less dependent on live coral habitats, such as Sheepfishes (Labridae), decreased significantly. These findings suggest a gradual recovery of fish resources following reef reclamation, with increases in large carnivores and coral-associated taxa, and declines in non-coral-dependent taxa. Continuous long-term monitoring is essential for elucidating fish community succession patterns and is critically important for promoting the health and resilience of coral reef ecosystems.