Population and life history features of the crab Aratus pisonii (Decapoda : Grapsidae) in a subtropical estuary

Population features of the grapsid crab Aratus pisonii, a common inhabitant of the supralittoral zone of roots, branches and canopy of several species of mangroves, were studied in two estuarine mangrove forests near Bertioga , Sao Paulo, Brazil, Crabs were larger in Bertioga-D (range: 8.85 - 26.20 m m), where a well-developed mangrove forest is present, than in nearby Berti oga-Cidade (range: 3.80 - 20.85 mm), where arbustive and stunted mangrove t rees prevailed. Ovigerous females were present at both sites; the percentag es in Bertioga-D and in Bertioga-Cidade were similar, 31.0% and 32.1%, resp ectively; however, the mean number of eggs was larger in Bertioga-D than in Cidade, 15,367 (maximum: 33,533) and 10,433, (maximum: 19,994) respectivel y. Abundances of A. pisonii were similar in the two study sites: 1.63 indiv iduals/m(2) in Bertioga-D and 1.41 in Bertioga-Cidade. Females were signifi cantly more abundant than males in a ratio of 1.168:1.00 in Bertioga-D, and 1.153:1.00 in Bertioga-Cidade. J-shaped sex ratio curves were observed for both populations. Juvenile crabs were present at both locations, but they were much more abundant in Bertioga-Cidade (34.8%) than in Bertioga-D (3.9% ), possibly as a consequence of the topography of each site. This study in a subtropical estuary suggests that a conceptual model presented previously , relating population features of A. pisonii and structural characteristics of mangroves forests for various localities on the Venezuelan coast, could be extended.