Do human impacts and environmental factors shape intertidal meiobenthic communities across freshwater, estuarine, and oceanic beaches in Uruguay?

Meiofauna comprises small benthic metazoans that play a crucial role in aquatic ecosystems and reflect the ecological condition of marine, estuarine, and freshwater environments. In this study, intertidal meiobenthiccommunities were examined across three coastal environment types along the Uruguayan coast (freshwater,estuarine, and oceanic), and the influence of anthropogenic impact on biodiversity and community structure wasevaluated. Three pairs of dissipative sandy beaches were sampled (one impacted and one less impacted perenvironment type), and the main meiobenthic taxa were quantified, calculating richness, Shannon exponentialdiversity, Pielou’s evenness, total abundance, and nematode abundance. Physicochemical water variables(dissolved oxygen and pH) and sediment characteristics (mean grain size and organic matter content) were alsomeasured. Generalized linear models showed that biodiversity indices were significantly associated withsediment properties and water parameters, with richness and abundance increasing in finer sediments and withhigher organic matter content, and diversity and evenness decreasing under higher organic enrichment. Dissolvedoxygen was positively related to richness, Shannon exponential diversity, and evenness. Nematodes, copepods,gastrotrichs, turbellarians, and nauplii dominated the assemblages, with nematodes being the most abundantgroup overall. Multivariate analyses (NMDS based on Bray–Curtis dissimilarities, PERMANOVA, and beta-dispersion) revealed a clear structuring of communities according to environmental type and the level ofanthropogenic impact. In particular, the group of less impacted beaches exhibited a more homogeneouscommunity composition (lower dispersion), whereas impacted beaches showed greater heterogeneity (higherdispersion), reflecting increased variability in composition among their samples. Indicator value analysis identifiedtaxa associated with specific environments and impact levels. Overall, these results highlight that meiobenthiccommunities on Uruguayan sandy beaches respond to both natural environmental gradients and humandisturbance, supporting the use of meiofauna as a sensitive tool for coastal ecosystem assessment