Modulating factors influencing abundances and distribution of brachyuran communities (Crustacea, Decapoda, Brachyura) close to the islands in Ubatuba, Brazil

The temporal and spatial variation of a benthic brachyuran assemblage in Sao Paulo, Brazil, showing patterns possibly explainable by various environmental factors: water temperature and salinity, organic matter and sediment texture was investigated. Samples were collected near the areas with unconsolidated substrates close to Couves (CO) and Mar Virado (MV) Islands, Ubatuba coast, São Paulo State, over a period of two years (January 1998–December 1999). Monthly sample collections were performed using a shrimp fishing boat equipped with a double-rig trawl. Temperature and bottom water salinity were measured monthly, whereas organic matter and sediment texture was measured seasonally. Environmental variables were compared among islands, seasons, and years using Permutational Analysis of Variance (Permanova) and Principal Component Analysis (PCA) analyses. Total Brachyura abundance was compared among islands, seasons, and years. For each island (CO and MV) the abundance was related to environmental variables, seasons, and years through Generalized Additive Models for Location, Scale and Shape (GAMLSS). In total, 2,109 samples were collected (1,021 in 1998 and 1,088 in 1999). The most abundant species were Hexapanopeus paulensis in CO and Callinectes ornatus in MV. The abundance of crabs was lower in CO than in MV. Such observations can be explained by the strong influence of oceanographic and continental events on CO. The reduced hydrodynamics at MV could promote fine sediment gathering and explain the homogeneous physicochemical characteristics of the area. Hence, different conditions can modulate species composition and abundance. This study provides information on the combination of modulating variables in benthic communities of brachyurans.