Continental slope fishes of the Potiguar Basin off Northeast Brazil in the Equatorial Atlantic ocean

Abstract

Deep-sea fish species compose around 15% of the observed fish biodiversity, and studies concerning the ecology and distribution of these marine fish species are essential to understand the magnitude of human influence on the deep ecosystems. The western South-Atlantic deep-sea fishes are well described and began to be studied in 1873. Nevertheless, studies considering fish community structure are still scarce in this area. This present study analysed the effects of oceanographic variables on deep-sea fish assemblages structure, density and species richness. To measure diversity, interpolated and extrapolated accumulation curves were drawn using Hill numbers along the Southwest Equatorial Atlantic Ocean depth intervals. A total of 36 trawls were carried out by an otter-boarded bottom trawl net between depths of 150 and 2000 m. Fish biomass showed the highest values between 150 and 400 m, reaching the highest numbers at 400 m, with a decline in the areas of 1000 m and 2000 m. The highest species richness was seen in the shallowest areas (150 m), with a declining trend towards deeper regions. Fish assemblages and habitats' affinity, species, individual lengths, depth, coast distance, longitude and density were used to identify and quantify clusters. The caught fishes belonged to 167 species (115 demersal, 52 pelagic), distributed within 63 families and three orders. The spatial and bathymetric occurrences of some species in the present study were broadened. The most important species in 150, 400, 1000 and 2,000m depth strata were Citharichthys cornutus, Saurida caribbaea, Monomitopus americanus and Dibranchus tremendus, respectively. Assemblages were clustered in four groups; the cluster's richness values were 64, 30, 10, and 11, respectively. Clusters 1, 2 and 3 represented depth values of 150, 400 and 1000 m and overlapped in k-means, showing a more similar pattern, unlike cluster 4 (2,000m). The most profound fish assemblage varies statistically significantly by depth, density, richness and diversity. Rapoport's rule interpretations explained the negative relationship between richness, density and depth and the positive association of length and depth. Despite the highest richness in cluster 1 and the lower richness in 4, they had the lowest effective diversities (Hill numbers), cluster 3 showed the lowest richness, but it had a high evenness trend and then had the highest effective diversity.