Local-scale distribution and habitat filtering of annelids in a subtropical estuary

Recording the small-scale distribution of organisms in changing environments is crucial for understanding local ecological patterns. We surveyed annelids from mangroves across different estuarine environments (open areas as unstable environments; control and closed areas as more stable environments) and habitats (vegetated, non-vegetated, and transitional zones) at Ararapira Inlet, Guaraqueçaba, Paraná, Brazil. During spring and autumn, we collected 288 samples using a corer, with a 0.5 mm mesh to separate fauna from sediment. We identified 937 individuals across 33 species, 18 families, and 28 genera, with Nereididae being the most represented family. The nereidid species Laeonereis acuta and Nereis oligohalina were the most abundant, with 254 and 149 individuals, respectively. Regarding endemism, 17 species are native and eight are non-indigenous, while information is lacking for seven. Our Linear Mixed Model showed that both abundance and species richness were generally lower in Control and Open areas, as well as in vegetated habitats, with positive interactions between area and vegetated habitats. The Control area exhibited higher Shannon diversity and evenness, while Simpson diversity was higher in the closed area. The transitional zone had the highest richness (23 taxa), followed by the non-vegetated habitat (19) and the vegetated habitat (14). Differences in Shannon and Simpson diversity were observed among areas, with the most established environments displaying the highest diversity. Microphage was the dominant feeding mode, with 15 taxa (46%), followed by omnivory with ten (30%), and macrophage with eight (24%). We conclude that the species respond to a complex combination of spatial scale and environment type, reinforcing the need to consider multiple ecological drivers when analyzing community structure.