Environmental filtering and spatial structure drive nestedness–turnover dynamics in bivalve mollusk metacommunities in the Atlantic continental margin of South America, Brazil

Abstract Species distributions along environmental gradients may exhibit nestedness, turnover, or clumping patterns. In environments subject to strong environmental variability, such as continental shelves, environmental filters exert a decisive influence on community composition, which may alternate across seasonal periods, leading to temporal variations in the structure and diversity of marine communities. This study aimed to investigate the organizational patterns of the metacommunity at small (north, central, and south sectors) and large spatial scales (continental margin) during two seasonal periods along a depth gradient on the northeastern Brazilian continental margin. Taxonomic α-diversity was higher in the southern sector and during the rainy periods. β-Diversity did not differ among sectors, but species composition exhibited high dissimilarity, particularly between the northern–southern and central–southern sectors, reflecting stronger species turnover during the rainy season, whereas richness differences predominated in the dry period. The metacommunity structure along the environmental gradient was predominantly Gleasonian at smaller spatial scales, with individualistic species responses and gradual shifts in composition, whereas quasi-Clementsian patterns emerged at broader scales, revealing groups of species with similar distributional limits and abrupt compositional changes. The metacommunity was primarily structured by environmental filters, with depth and gravel as the main predictors. Spatial processes had a limited influence and were associated with dispersal limitation, whereas most of the variation remained unexplained by the measured variables. Overall, the results indicate that environmental filtering (depth and gravel) constitutes the primary structuring mechanism, acting in conjunction with large-scale spatial effects associated with dispersal limitation and mass effects acting at smaller-scales.