A dataset on trophic structure and stable isotope composition in a moderately eutrophic Halophila beccarii seagrass ecosystem in Huachang Bay, China

This dataset compiles trophic, ecological and isotopic information for macrozoobenthos and nekton associated with a Halophila beccarii seagrass meadow in Huachang Bay, Chengmai, Hainan, China, as described in the accompanying research article. The data were generated from field sampling in the seagrass bed, taxonomic identification of macrozoobenthos and fishes, literature-based compilation of dietary and habitat information (primarily from FishBase and SeaLifeBase), and stable isotope analyses (δ¹³C and δ¹⁵N) combined with Bayesian mixing models (MixSIAR) and isotopic niche metrics to quantify trophic positions and carbon-source contributions. Table S1 provides species-level information on the dietary composition of macrozoobenthos and nekton. For each taxon (rows), the table reports the species name, a concise description of its distribution and ecological habits, its assigned nutritional (trophic) functional group (e.g., Bivalves, Herbivorous gastropods, Carnivorous fishes), and the data source used to derive feeding and habitat traits (FishBase, SeaLifeBase or primary literature). This table allows users to trace how each consumer was assigned to a functional group and to reuse these trait assignments in other food-web or functional-diversity analyses. Table S2 summarizes the trophic groups of macrozoobenthos and nekton in the Huachang Bay seagrass bed. For each functional group, the table lists the species composition, the number of species included, the number of isotopic samples, a qualitative description of diet composition and feeding habits, and the trophic position category (e.g., primary consumers, secondary consumers, secondary/tertiary consumers) inferred from δ¹⁵N values in this study. This table links taxonomic composition with feeding guilds and trophic levels, and can be reused to define consumer groups for other modelling exercises or comparative studies. Table S3 reports the group-specific trophic levels (mean ± SD) and trophic enrichment factors (TEFs; Δδ¹³C and Δδ¹⁵N, in ‰ per trophic level) used in the sensitivity MixSIAR scenario for the Huachang Bay seagrass bed. Each row corresponds to one functional group (e.g., Zooplankton, Bivalves, Carnivorous fishes) and includes the number of samples, the estimated trophic level, and the TEFs applied in the mixing-model runs. These values enable users to reproduce or modify the Bayesian mixing-model analyses, or to test alternative TEF scenarios in their own work. Figure S1 illustrates the contribution rates of organic carbon sources to the main consumer groups (n ≥ 4) in the H. beccarii meadow of Huachang Bay, based on MixSIAR posterior estimates. The figure shows the relative contributions of different basal sources (e.g., seagrass, epiphytes, macroalgae, particulate and sediment organic matter, mangroves) to each major consumer group, providing a synthetic view of the seagrass-associated benthic food web. All tabular data are provided in machine-readable format (e.g., .csv or .xlsx), with each row representing a species or functional group and columns corresponding to traits, diet descriptors, isotopic metrics and model parameters. No intentional missing values are included in these summary tables; any empty cells reflect information that could not be reliably extracted from the literature. This dataset can be directly reused to parameterize food-web models, to compare trophic structures across ecosystems, or to build meta-analyses on seagrass-associated consumer guilds and trophic dynamics under eutrophication.