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

Abstract

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 meiobenthic communities 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 was evaluated. Three pairs of dissipative sandy beaches were sampled (one impacted and one less impacted per environment type), and the main meiobenthic taxa were quantified and richness, Shannon diversity, Pielou’s evenness, total abundance, and nematode abundance were calculated. Physicochemical water variables (dissolved oxygen and pH) and sediment characteristics (mean grain size and organic matter content) were also measured. Generalized linear models showed that biodiversity indices were significantly associated with sediment properties and water parameters, with richness and abundance increasing in finer sediments and with higher organic matter content, and diversity and evenness decreasing under higher organic enrichment. Dissolved oxygen was positively related to richness, Shannon exponential diversity, and evenness. Nematodes, copepods, gastrotrichs, turbellarians, and nauplii dominated the assemblages, with nematodes being the most abundant group 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 of anthropogenic impact. In particular, less impacted beaches exhibited a more homogeneous community composition (lower dispersion), whereas impacted beaches showed greater heterogeneity (higher dispersion), reflecting increased variability in composition among their samples. Indicator value analysis identified taxa associated with specific environments and impact levels. Overall, these results highlight that meiobenthic communities on Uruguayan sandy beaches respond to both natural environmental gradients and human disturbance, supporting the use of meiofauna as a sensitive tool for coastal ecosystem assessment.