Asymmetric effects of changes in the habitat‐forming algae Sargassum on different associated mobile faunas along São Paulo coast, Brazil

Abstract

Macroalgae constitute an important habitat for several marine invertebrates, and their biomass and structural complexity modulates the abundance and diversity of species that live on them. Overall, fluctuations in algae biomass inflict fluctuations in the abundance of the associated mobile macrofauna, but the structure of the community may vary according to how each group/species uses the resources provided by the algal habitat. Here, we evaluated how temporal variations in the biomass of Sargassum algal bed (increase, decrease, or maintenance) can affect the abundance, density, and assemblage structure of distinct associated faunistic groups. The collections were performed in three rocky shores located on the north coast of São Paulo, southeastern Brazil, during Fall and Spring. We observed different patterns of algal substrate variation between sampling events, and this reflected on variable effects on the associated fauna. The algal substrate reduction was accompanied by the reduction in the abundance and density of all associated faunal groups. However, the increase or maintenance of the algal substrate was accompanied by an increase in the abundance of peracarids, due to the dominance of herbivorous species, while other taxonomic groups like mollusks and polychaetes decreased or maintained their abundance, although with higher species evenness of gastropods when alga increases. Seasonal biomass variations in macroalgae beds are relevant for the dynamics of its associated fauna, and our results indicate that some taxonomic groups may preferentially use the available extra resources originated from biomass increment when compared to other groups.

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