Biologia populacional de Chasmagnathus granulatus Dana, 1851 (Crustacea, Decapoda) na Baía de Guanabara, RJ

Abstract

The aim of this work was to get knowledge about population biology of Chasmagnathus granulatus Dana, 1851 of the APA Guapimirim mangrove in Guanabara Bay, RJ. Three areas were determined and monthly sampling were did during low tides using CPUE, with one collector during 15 min in each area. The samples took place from july/2005 to june/2006. Juveniles were captured by quadrat, with five samples for each area. At the laboratory, the crabs were sexed and measured with a vernier caliper (0,01 mm) and the gonads, gonopods and abdomen morphology were observed according to shape and macroscopic aspects. A total of 1,049 specimens were sampled and were recognized five morphotypes: immature males (23), mature males (438), immature females (83), mature females (306) and juveniles (23). 160 juveniles were collected by quadrat too. The spatial-temporal distribution was verified by number of caught crabs along of the months and the studied areas. The crabs were frequent during all period and they occurred in all the areas. Ovigerous females and juveniles demonstrated preference for area 2. The population structure was analyzing by the frequency distribution of the size class (08 class of size, with 5.0 mm each). Males were similar than females (males 20,39 ± 5,98 and females 19,2 ± 5,26 mm of carapace width) and they had the larger class of size (28,8-32,4 e 32,4-36,0 mm). The distribution of the size frequency was unimodal to males and females (20,1-25,0 mm), and both showed growing on springsummer. The sex ratio is near 1:1, with males predominance in area 1 and in October/2005 and april/2006. The recruitment occurred on spring. The breeding season was verified by of ovigerous and no ovigerous females number and it occurred on winter. There is a inverse correlation between breeding season and environmental factors. The fecundity was estimated by sub samples of the egg mass dissociated. The mean of the egg size was 0,23 ± 0,01 mm and the mean of volume was 0,0065 ± 0,01 mm3 and the growing of both is related with development stages. The mean of fecundity was 25.185 ± 15.050 eggs. The physiological maturity in males revealed similar values of carapace (17,2 mm) with relation to those obtained with morphometric analysis (17,19 mm and 14,4-18,0 mm). In females the physiological maturity occurred with 18,9 mm and the morphometric maturity showed two inflexion points: 17,96 e 22,48 mm. The present study to make possible to conclude about C. granulatus Piedade s population: the structure of microhabitat is important to individuals distribution, the seasonal breeding and recruitment can be associated with females bimodal distribution; and the high reproductive potential and larger size of individuals could be associate with the major organic matter entrance inside Guanabara Bay waters.