Steroid hormones, recognized as emerging environmental contaminants, have garnered increasing attention in recent years. The present work studied the distribution characteristics in the environment, bioaccumulation in aquatic products, and the associated environmental and health risks of typical steroid hormones from commercial freshwater aquaculture farms operating under different aquaculture modes (monoculture and polyculture). Totals of 9 and 14 steroid hormones were detected in water and sediment samples, with concentrations ranging from 0.66 ± 0.17 ng/L to 40.5 ± 5.08 ng/L and from 0.36 ± 0.08 ng/g to 123 ± 19.9 ng/g, respectively. Hazard index (HI) calculations indicated that all sampling locations were identified as medium or high risk for both water and sediment matrices. Nineteen steroids were detected in at least one type of tissue, with the concentrations in the bile, plasma, muscle, liver, and gill ranging from <LOQ to 52.6 ± 4.82 ng/L, from <LOQ to 41.9 ± 4.80 ng/L, from 0.36 ± 0.07 ng/g to 321 ± 19.1 ng/g, from 5000 L/kg). Notably, despite low estimated daily intakes (EDIs) (0.43–6.43 ng/day/person to 18.7 ng/day/person) and hazard quotients (HQs) (below 4.188 × 10⁻⁷), the high bioaccumulation factors (BAFs) underscore the necessity for stringent regulatory measures by local governments. Additionally, a comparison of EDI results across different aquaculture modes and fish species revealed that steroid hormone-related health risks to humans are influenced by both the fish species and the aquaculture mode. This study indicated that the consumption of poly-cultured fish (e.g., bighead carp) may pose a greater steroid-related health risk, compared to the consumption of mono-cultured fish.

Exploring the response of the diversity of phytoplankton species and functional groups to environmental variables is extremely important in maintaining biodiversity in aquatic ecosystems. Although there were more taxonomic units at the species level than at the functional group level, it remained unclear whether species diversity was more sensitive than functional group diversity to environmental variables. In this study, taxonomic composition and alpha–beta diversity of phytoplankton were investigated in 23 subtropical reservoirs located in the Han River Basin in South China during wet and dry seasons. Structural Equation Modelling (SEM) and Generalized Dissimilarity Modelling (GDM) were employed to validate the response of phytoplankton species and functional group alpha–beta diversities to environmental variables. The results indicated that the community compositions of phytoplankton in eutrophic reservoirs were similar between wet and dry seasons, while there were distinct differences for community composition in oligotrophic–mesotrophic reservoirs between the two seasons. Across all reservoirs, there were no significant differences in alpha and beta diversities of species and functional groups between wet and dry seasons. The SEM and GDM results revealed that total phosphorus was the primary driving factor influencing alpha and beta diversities of species and functional groups in the 23 reservoirs. Meanwhile, the non-linear results of species beta diversity were stronger than the non-linear results of functional group beta diversity, indicating that phytoplankton species exhibited a higher explanatory power in responding to environmental changes compared to that of functional groups. Compared to that of species beta diversity, the response of functional group beta diversity to environmental variables was significantly lower in the dry season. These research findings lead to re-evaluating the common practice relating to the use of phytoplankton functional groups to assess environmental conditions, which may overlook the explanatory power of subtle changes at the species level, especially during periods of habitat diversification in the dry season.

As a typical turbid-water reef coral, Turbinaria peltata shows strong tolerance to high temperature and sediment disturbance, yet its basin-scale niche drivers and glacial distribution dynamics across the Indo-West Pacific remain unclear. Here we constructed optimized MaxEnt models using 322 independent distribution points and 21 non-collinear marine environmental variables for modern and Last Glacial Maximum (LGM) scenarios. The model average test AUC reached 0.9874, showing excellent predictive performance. Water depth acted as the most influential predictor in the model (contribution = 44.76%), followed by distance to land and warm-season sea temperature; habitat suitability had an extremely weak linear correlation with depth (R² = 0.05), consistent with a strongly nonlinear response along the depth gradient. Modern suitable habitats are mainly concentrated in Southeast Asia and northern Australia, with the South China Sea at the species’ northern margin. Massive shelf exposure during the LGM severely shrank its range, and three potential glacial refugia (northeastern Australia, Madagascar coast, Red Sea–Gulf of Aden) were identified. These refugia may have maintained coral populations through glaciation and contributed to the present-day biogeographic patterns of this species. Our findings provide quantitative spatial evidence for targeted conservation of nearshore stress-resistant corals under climate warming.

The tri-spine horseshoe crab, Tachypleus tridentatus, is an evolutionarily ancient marine chelicerate of considerable ecological and conservation importance in the Indo-West Pacific. Although several mitochondrial genomes have been reported, comprehensive comparative mitogenomic analyses encompassing all extant limulid genera remain limited. In this study, we sequenced and characterized the complete mitochondrial genome of an F1 Tachypleus tridentatus individual derived from wild-caught broodstock from the Beibu Gulf, northern South China Sea, and subsequently maintained at an aquaculture facility, using high-throughput sequencing, and performed an integrated comparative mitogenomic analysis across the three extant genera of Limulidae. The circular mitochondrial genome was 15,006 bp in length and contained the typical set of 37 mitochondrial genes, including 13 protein-coding genes (PCGs), 22 transfer RNA genes, and two ribosomal RNA genes. The newly sequenced Tachypleus tridentatus mitogenome showed highly conserved genome organization and nucleotide composition relative to previously published conspecific mitogenomes, confirming established mitochondrial characteristics of the species. The principal contribution of this study is the addition of a complete Beibu Gulf mitogenome and its integration with 12 additional complete mitochondrial genomes representing all extant limulid species, together with four mitochondrial markers, K2P genetic-distance analyses, and independent BI and ML phylogenetic reconstruction. The concordance among these mitochondrial datasets provides an integrated assessment of genetic divergence and mitochondrial phylogenetic relationships within Limulidae and expands the geographic representation of complete mitochondrial genomic resources for Tachypleus tridentatus.

Coastal waters of eastern Guangdong are important fishing grounds and ecologically sensitive areas in the northern South China Sea, where nekton communities are increasingly affected by environmental heterogeneity and human activities. However, systematic studies on the spatial differentiation and driving mechanisms of nekton communities in this region remain insufficient. This study aimed to clarify the community structure, diversity distribution characteristics, and key driving environmental factors of nekton in the coastal waters of eastern Guangdong, and thereby provide scientific support for an ecological health assessment and sustainable utilization of fishery resources in this region. Based on bottom-trawl survey data from 19 stations in the coastal waters of eastern Guangdong, northern South China Sea, this study systematically analyzed the species composition, dominant species, and diversity distribution pattern of nekton and their correlations with environmental factors using methods including the Index of Relative Importance, Alpha diversity indices, Beta diversity indices, and redundancy analysis. A total of 119 nekton species belonging to three phyla, four classes, 14 orders, and 56 families were collected. Among them, there were 79 fish species (accounting for 66.39%), 36 crustacean species (30.25%), and four cephalopod species (3.36%). The dominant species were Trachypenaeus curvirostris and Portunus sanguinolentus (IRI ≥ 1000). Wilcoxon’s test showed that there were significant differences in the Shannon–Wiener index, Gini–Simpson index, and Pielou’s evenness between the nearshore and offshore groups, while no significant regional difference was observed in the richness index. Cluster analysis, based on the Bray–Curtis distance, divided the 19 stations into five clusters, with significant differentiation in species composition and functional structure within the nearshore group. RDA results indicated that environmental factors collectively explained 99.66% of the variation in community structure. Particulate Inorganic Carbon (PIC), Phosphate (PO₄³⁻), Distance to Port, Summer Maximum Chlorophyll-a (Chl-a), and Total Suspended Matter (TSM) were identified as the key driving factors. The coastal waters of eastern Guangdong boast rich nekton species, with significant differences in community structure between nearshore and offshore areas. The heterogeneity of the natural environment and human activity disturbances jointly shape the nekton diversity pattern in this region. The research results can provide a theoretical basis for regional marine ecological protection and fishery resource management.