Effect of bathymetric gradients on the diversity of demersal fish in the region of Ilha de Queimada Pequena – Peruíbe – SP G. C. Stabile, D. B. V. L. Souza, G. A. Torres, H. V.P.M. Silva, J. P. Santos, L. S. Bernal, V. Masson, A. A. Liberati, R. A.O. Souza, M. E. Laranjeira, M. M. Rotundo

Abstract

Changes in distribution patterns may anticipate changes in demersal fish communities. Therefore, knowledge of community dynamics and their ecological interactions at spatial and temporal scales is necessary, due to regional and seasonal variations, mainly to support adequate resource management. The present study aimed to evaluate the effect of bathymetric gradients on fish diversity in the region of Ilha de Queimada Pequena, in the municipality of Peruíbe – SP. The collection was carried out in August 2016, in the region between the mainland and the island, at four points parallel to the beach, at different depths (5.5; 6.5; 9 and 11 meters), using a shrimp boat with a net. door drag. All specimens were identified and measured for weight (g) and total length (mm). Based on abundance and richness, Shanonn's diversity indices (H'), Margalef's richness (Mg), Pielou's equitability (J'), dominance (D), rarefaction curve, Jaccard's similarity and “t” test were calculated. ” of diversity, seeking to highlight differences between depths. All calculations were performed using the PAST program (Palaeontological Statistics, version 2.17). 980 specimens belonging to 22 species and 12 families were captured. The highest values ​​observed for H' and J' were related to the shallower depth (5.5 m), as well as the lower D value and number of specimens captured. The lowest values ​​for H', Mg and J' occurred at the greatest depth (11 m), where the highest values ​​for D and number of specimens were also observed. Neither month reached the asymptote on the rarefaction curve. The greatest similarity in composition (60%) occurred between depths of 6.5 and 11 meters, and the lowest (40%) between 5.5 and 11 meters. The diversity “t” test showed a significant difference (p<0.05) between the deepest point (11 m) and the others. Based on the results, it was possible to observe a decreasing pattern of diversity in relation to increasing depth, or even the same pattern for the distance between the continent and the island. It is worth noting that the observed variation must also be analyzed seasonally to gain effective knowledge of the region's fish community, which could even mitigate the results of this study.