Biótopos bentônicos no litoral setentrional do nordeste brasileiro, Macau – RN, Brasil

Abstract

The environments found on the continental shelf of Rio Grande do Norte, located in northeastern Brazil, are highly heterogeneous, being important suppliers of habitats that help to compose a rich biodiversity. Thus, inserted in the INCT AmbTropic, the objective of the present study was to characterize the benthic biotopes, mapping their distribution on a spatial and temporal scale in different unconsolidated seabed of the northern platform of northeastern Brazil. Sampling was carried out in May / 2014 (rainy) and December / 2014 (dry), in three environments: Oeste do Açú (OA), with bioclastic sands; Vale do Açú (VA), with terrestrial sludge and; Leste do Açú (LA), with silicibioclástica and biosiliciclastic sands. Altogether, 30 transects were performed, 5 in each of the environments (for periods) through bottom trawling with the aid of a motorized fishing vessel totaling 1171.5 m². All benthic fauna on the surface of the marine sediment was collected and fixed in 70% alcohol and identified at the species level. The values ​​of density and biomass were tested using 2-way ANOVA and a posteriori test of Ficher LSD, and a data matrix was elaborated from the Bray-Curtis index in order to evaluate the formation of groups in relation to the composition of the taxa with a n-MDS, tested using ANOSIM. The taxa most contributing to the formation of the groups shown with SIMPER. The most representative groups were Echinodermatas, Molluscs and Crustaceans in both periods. The density varied significantly over the periods and areas (LA and OA, p <0.005), except for VA. Biomass, on the other hand, did not show any significant difference between the periods within LA and VA, but there was a significant difference between rainy and dry conditions within OA, explained by the large concentration of P. imbricata mollusks within this environment. The richest areas were LA in the rainy season and OA in the dry season. The SIMPER analysis showed that the species that contributed most to the separation of the groups were: Leodia sexiesperforata (24%) and Encope grandis (12%) in LA; Amphipoda spp. (40%) and Pinctada imbricata (17%) in bioclastic sands (OA) and Strombus pugilis (62%) in terrestrial muds (VA), this for the rainy season. In the dry period, there was an inversion of groups in LA, with Lytechinus variegatus (49%); Pinctada imbricata (74%) in the bioclastic environment (OA) and, in the environment with terrestrial sludge (VA), the species Callinectes ornatus with 50% was the most relevant, showing that the composition or assembly of benthic organisms depends on heterogeneity and / or complexity of habitats. Thus, the present study showed that the type of sediment plays an important role in the structuring of epifauna communities on the Continental Shelf of Macau-RN, and can be used as an important factor in defining the habitats of these organisms in the unconsolidated bottoms.