Beta diversity of demersal fish and implications for conservation in a subtropical environment

The present study aimed to evaluate the variation in the composition and diversity of the fish assemblages (beta diversity) along the east-west axis of the Paranaguá Estuarine Complex and the Adjacent Continental Shelf. To this end, seasonal collections were carried out between 2014 and 2016 at 12 sampling sites, totaling 144 collections. These sites were distributed in 4 sectors (External, Lower, Middle, and Upper) on an axis from the continental shelf to the interior of the estuary. Beta diversity (βSOR), calculated by the Sørensen index, was divided into the components turnover (βSIM) and nestedness (βSNE) and evaluated the contributions of each to the total heterogeneity. βratio, the ratio of βSNE to βSOR, was estimated to identify the components with the greatest contribution to the total beta diversity. To corroborate the results, nestedness estimates were made using the NODF (Nestedness metric based on Overlap and Decreasing Filling), compared to the null model. For the Upper, Lower, and External sectors, βratio values were lower than 0.5, indicating that the turnover was predominant for variations in total beta diversity, as expected for these environments. Unlike the other sectors, in the Middle sector, βratio values were greater than 0.5, indicating that nestedness was predominant for variations in total beta diversity, which may reflect possible natural or human stressors since innumerable disturbances have already been detected in this environment.