Macroalgae constitute an important habitat for a wide variety of marine invertebrates in coastal ecosystems, which can obtain food, refuge against predators, protection against environmental stress and sites for reproduction, and/or larval settlement (Christie et al., 2009; Thomaz & Cunha, 2010). Those small-sized associated animals have great ecological importance, as they also serve as food items for other larger coastal species such as fishes, thus acting as energy links among different levels in marine trophic webs (Donadi et al., 2017;Dulvy et al., 2002).The southeastern coast of Brazil has a great diversity of macroalgae, with about 50 species of different groups and growth forms

Anthropogenic impacts on coastal habitats can result in alterations of diversity parameters in marine invertebrate assemblages. Macroalgae beds are highly susceptible to human‐induced disturbances, supporting a great diversity of molluscan species and being ecologically important for coastal ecosystems. This study investigates the diversity alterations on Sargassum‐associated molluscan assemblages from areas with different distances from a main source of pollution within a historically impacted bay in Brazil. In general, sites closer to the pollution source presented lower species diversity, trophic diversity, and taxonomic relatedness among species. Beta diversity among assemblages was highly correlated with environmental differentiations among localities due to heavy metal concentrations in algal tissue. Bittiolum varium was the dominant species and was mainly responsible for differences in community parameters. Several trophic groups were well‐represented in Sargassum‐associated molluscan fauna, but assemblages were mostly dominated by micrograzers. A seasonal trend was observed in diversity alterations, with lower diversity during warm season at most sites except Santa Rita, possibly because it is the site less affected by human impacts. The importance of other environmental variables, such as hydrodynamism, for molluscan composition is also discussed. Our results highlight the potential of Sargassum‐associated molluscan assemblages for the study of impacted areas and reinforce the importance of using multiple community metrics to understand the biodiversity patterns of marine invertebrates under anthropogenic impacts.

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A Enseada do Flamengo, em Ubatuba (SP), possui áreas com histórico de contaminação causado por intensa atividade humana. Gastrópodes de algas são considerados bons bioindicadores, e o estudo dessas populações pode auxiliar nas interpretações do estado de conservação de um local. O objetivo deste trabalho é investigar a estrutura populacional do gastrópode Bittiolum varium, espécie abundante na região. Através da análise de diferentes populações, obtiveram-se dados de abundância e estrutura etária. As populações apresentaram mais indivíduos e maior número de juvenis nas praias mais expostas ao padrão de circulação de água da Enseada. A contaminação local, assim como o padrão de circulação das águas, possivelmente explicam os resultados obtidos.