Assessing sandy beach macrofaunal assemblages across geographically diverse morphodynamic environments.

While the physical characteristics of sandy beaches play a significant role in shaping the macrofaunal community features through morphodynamics, regional environmental factors may also account for deviations from the expected patterns. Here, we assess the concurrent effects of local morphodynamic factors and regional variables, such as sea surface temperature (SST), salinity, and chlorophyll-a (chl-a), on species richness and abundance of intertidal macrofaunal assemblages in four sandy beaches located along the estuarine gradient generated by the Río de la Plata (RdlP) in the southwestern Atlantic Ocean. Species richness was higher in dissipative beaches compared to intermediate ones, consistent with the predictions of the Swash Exclusion Hypothesis. However, this trend was not observed for total abundance, which significantly increased with chl-a. Both local and regional-scale environmental factors, such as salinity and chl-a, proved to be significant predictors in the arrangement of these communities. These results further support previous findings that highlight the critical role of the estuarine gradient of the RdlP in shaping life-history traits, population structure, and abundance of the resident intertidal macrofauna at both local and regional scales. The study underscores the importance of integrating environmental factors operating at different spatial scales to decipher community patterns in these physically-controlled environments.

Disentangling patterns in population parameters of the wedge clam Donax hanleyanus from sandy beaches of Argentina: The role of environmental variability.

The concurrent role of morphodynamics and estuarine gradients in shaping population patterns in sandy beach macrofauna has not been adequately assessed. Here, we analyze the effects of beach morphodynamics, salinity, sea surface temperature, and chlorophyll-a (chl-a) on life-history traits of the wedge clam Donax hanleyanus in four sandy beaches located along the estuarine gradient generated by the Río de la Plata (RdlP, Argentina) over a 13-month period. A general linear model showed that chl-a and salinity were positively correlated with the abundance of D. hanleyanus, whereas between-beach differences in individual size, population structure, and growth performance were mainly explained by salinity fluctuations. These results indicate that the estuarine gradient of the RdlP plays a critical role in shaping life-history traits, population structure, and abundance of D. hanleyanus at local to regional scales, overriding the effects of local characteristics of the habitat. The study highlights the importance of conducting multi-scale studies that integrate environmental factors to elucidate the main physical drivers of population patterns in sandy beach ecosystems.