POPULATION STRUCTURE AND REPRODUCTIVE BIOLOGY OF THE CRAB SESARMA RECTUM RANDALL, 1840 (BRACHYURA, SESARMIDAE) IN AN IMPACTED TROPICAL MANGROVE IN NORTHEAST BRAZIL

摘要

The population structure and reproductive biology of the semiterrestrial crab Sesarma rectum were studied in an impacted tropical mangrove in northeast Brazil. Crabs were collected monthly during spring low-tide periods from October 2009 through September 2010. A catch-per-unit-effort (CPUE) technique was used to sample the crab population, using two-hour sampling periods by two people. A total of 492 crabs was obtained, of which 262 were males, 151 non-ovigerous females, and 79 ovigerous females. Males were significantly larger than females, whether non-ovigerous or ovigerous. There was no significant difference between mean size of the ovigerous and non-ovigerous females. The population showed a unimodal size-frequency distribution, with a normal distribution for males and non-normal for females. The overall sex ratio (1 : 0.87) did not differ significantly from the expected 1 : I proportion. Ovigerous females were found during the entire period, except in March and August 2010. The mean number of eggs was 14975 +/- 5689. The highest number of eggs was recorded for the 29 to 31 mm age group. A regression analysis showed that the number of eggs increased linearly with carapace width (r(2) = 0.70) and abdomen width (r(2) = 0.76). Comparisons among populations will help to evaluate the differences among them, as well as to understand the environmental and biological constraints that are shaping them.