Diversidade taxonômica e funcional da macrofauna bentônica associada a bancos de rodolitos na plataforma continental Leste do Brasil

Abstract

Rhodoliths are free-living and morphologically diverse marine calcareous algae that are commonly distributed over the continental shelf seafloor. They increase seabed structural complexity and are of potential value as feeding and reproductive grounds for a myriad of marine fauna. The higher structural seabed complexity within rhodolith beds (RBs) may also increase overall benthic diversity by creating microhabitats, but this relationship has been rarely explored within RB worldwide. Here we compared benthic macrofaunal (> 500µm) structure RB (inside nodules) and within unconsolidated sediments under high and low-density beds to test whether benthic assemblages were associated with rhodolith bed density and nodule morphology. We observed that benthic diversity was higher in rhodoliths, whereas macrofaunal density was 16-fold higher when compared to sediments under RBs, which also displayed low nestedness and high taxa turnover between habitats. RB density and nodule morphology explained macrofaunal, taxonomic, and functional diversity in the rhodoliths. High-density RBs (204 ± 32.5 nodules.m-2 ) had a higher macrofaunal diversity (taxonomic and functional) and exhibited typically spheroidal nodules with higher internal volume, being dominated by Annelid polychaetes. In contrast, low-density RBs (61 ± 46.9 nodules.m-2) exhibited discoidshape nodules with a higher mean diameter and were dominated by peracarid crustaceans. Macrofaunal diversity, density, and functional diversity showed no differences between RBs densities, but macrofauna structure was influenced by the rhodolith beds, which increased carbonate content and sediment organic quality (protein and carbohydrates) in high-density stations. These findings indicate that benthic communities change markedly in response to RB density and nodule morphology, and provide critical habitat for several unique benthic species that are not encountered in unconsolidated sediment below these beds on continental shelf depths. This study highlights the importance of protecting habitat complexity as a key factor influencing macrofaunal diversity in rhodoliths areas.