Identifying key habitat and spatial patterns of fish biodiversity in the tropical Brazilian continental shelf

Knowledge of the spatial distribution of fish assemblages biodiversity and structure is essential for prioritizing areas of conservation. Here we describe the biodiversity and community structure of demersal fish assemblages and their habitat along the northeast Brazilian coast by combining bottom trawl data and underwater footage. Species composition was estimated by number and weight, while patterns of dominance were obtained based on frequency of occurrence and relative abundance. A total of 7235 individuals (830 kg), distributed in 24 orders, 49 families and 120 species were collected. Community structure was investigated through clustering analysis and by a non-metric multidimensional scaling technique. Finally, diversity was assessed based on six indices. Four major assemblages were identified, mainly associated with habitat type and depth range. The higher values of richness were found in sand substrate with rocks, coralline formations and sponges (SWCR) habitats, while higher values of diversity were found in habitats located on shallow waters (10–30 m). Further, assemblages associated with sponge-reef formations presented the highest values of richness and diversity. In management strategies of conservation, we thus recommend giving special attention on SWCR habitats, mainly those located on depths between 30 and 60 m. This can be achieved by an offshore expansion of existing MPAs and/or by the creation of new MPAs encompassing those environments. •We characterize the demersal fish composition of the main habitats found in Northeast Brazil.•We highlight the importance of Outer Shelf environments as an area of high fish densities and diversity.•Coralline habitats hold the highest number of endangered species and the greatest values of biodiversity.•Habitat composition and position on the Shelf Break are main factors that drive the assemblages structure.