Submarine outfall and new sewage treatment plant modulate the response of intertidal benthic communities in a SW Atlantic area

Abstract

Spatio-temporal responses of the intertidal macrobenthic community to the effects of a submarine outfall (SO) and a new sewage treatment plant (EDAR) were evaluated, analyzing changes in macrofaunal assemblages and community structure. Study was conducted in a SW Atlantic coastal area in 4 stages: B_SO (Before the SO), Du (During the construction of the SO), A_SO (After the SO start-up) and A_EDAR (After the treatment plant start-up). Boccardia proboscidea and Brachidontes rodriguezii contributed most to the differences between all stages at the site nearest to the discharge point. Number of individuals was highest at B_SO and Du. Richness and diversity were lowest at the B_SO and highest at the Du. Furthermore, the richness decreased slightly, and the diversity increased at A_EDAR. Evenness was highest at the B_SO and A_EDAR. The nestedness was the dominant process driving the differences between the B_SO stage community and the rest of the stages. SO affects the composition and structure of the intertidal macrobenthic community near the outfall area, as organic matter discharge further offshore favour the development of a more diverse intertidal community, including species sensitive to organic enrichment.

Keywords: Alpha diversity; Biotic indices; EDAR; Intertidal macrobenthos; Sewage discharge; beta diversity.