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

Resumo

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, calculating richness, Shannon exponential
diversity, 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 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, the group of 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