Decadal Variability in the Structure of Benthic Fauna of Subtropical Salt Marshes and Unvegetated Areas

Over a decade (2013 to 2022), we investigated the variability of benthic macrofauna in two distinct environments characterized by contrasting structural complexities: salt marshes and adjacent unvegetated areas. We also evaluate the influence of eight teleconnection patterns in environmental variables in southern Brazil. We collected 58,818 organisms, distributed in 52 morphospecies, with an overlap of 63.5% of species between habitats. Our results indicate that positive periods of teleconnection patterns, such as Oceanic Niño Index (ONI) and the Pacific Decadal Oscillation (PDO), significantly impacted macrofauna density and structure, especially in unvegetated habitats where density reached peaks of 567 inds/0.03m² during the El Niño events (2015–2016). Two opportunistic species, Monokallipseudes schubarti and Laeonereis acuta, represented more than 50% of all macrofauna and were responsible for density peaks over habitats in periods of positive anomalies (summer, 9.822 inds/m²; winter, 3.017 inds/m²). In general, unvegetated habitats exhibited higher macrofauna density, while salt marshes showed greater interannual homogeneity. As a result, we observed that salt marshes provided more beneficial conditions for macrofauna, maintaining consistent community structures, that reinforce the critical role of El Niño events in modulating benthic assemblages and the importance of salt marshes as resilient habitats in the face of climate anomalies.