Submarine outfall effect on subtidal macrobenthic communities in a southwestern Atlantic coastal city

Submarine outfalls are an effective alternative for the final discharge of wastewater. The aim was to evaluate the subtidal macrobenthic community's responses and the changes in bottom sedimentary dynamics due to submarine outfall (SO) location. Sampling stages were: before SO (B(SO)), after SO (A(SO)) and after treatment plant (A(EDAR)). Sampling sites were determined at different distances from the coastline (coastal, oceanic, and reference) on both sides of the pipe (North and South). Species shifts (from tolerant to sensitive) were observed along with a decrease in organic matter in the A(EDAR) Stage. There were changes in the sedimentary dynamic with sediment accumulation on the South side of the SO (finest sediments) and erosion on the North side (coarsest sediments) in the A(SO) and A(EDAR) Stages. Species turnover was higher than nesting in all stages. Functional trait analysis allowed the identification of temporal variations in benthic communities. The body size, development mode, feeding mode, habit, adult mobility and tolerance to pollution were useful functional traits to detect changes through Stages (B(SO), A(SO), and A(EDAR)). Biotic indices classified the sites as slightly disturbed, indicating a slight improvement in the A(EDAR) Stage.