Linking taxonomic and functional diversity of the macrobenthic community to a depth gradient in a sandy shore ecosystem of the SW Atlantic Ocean

Abstract

This work investigates the depth-related distribution patterns of macrobenthic communities in a sandy shore ecosystem. We analyse changes in community descriptors and biological traits and the importance of wave effects on the macrobenthic community [wave exclusion hypothesis (WEH)] at three different depths: in the inner surf zone at approximately 1 m, and in the nearshore zone at 5 m and 15 m. A total of 130 taxa, primarily Arthropoda, Annelida, and Mollusca, were collected across depths. Following the WEH, abundance and biomass increased with depth, reaching their highest values at 15 m. Richness and diversity were significantly higher at intermediate depths, where the presence of both sandy and rocky substrates supported a more diverse community. Species turnover dominated beta diversity patterns, indicating important species replacement across the depth gradient, especially between the shallow surf zone and deeper subtidal areas. Biological traits analysis revealed that mobile, detritivorous, and deposit-feeding organisms dominated the surf zone, while sedentary, filter-feeding, and omnivorous organisms characterised deeper areas. These distribution patterns are linked not only to the contrasting wave action but also to the sedimentary conditions along the depth gradient. These results provide key insights into the influence of depth on the structure and composition of macrobenthic communities in sandy shore ecosystems, revealing distinct biological zones across the depth gradient and emphasizing the role of substrate characteristics in shaping benthic assemblages.