Population structure of the fiddler crab Uca leptodactyla Rathbun, 1898 (Brachyura: Ocypodidae) in a tropical mangrove of northeast Brazil

Abstract

The population structure of the fiddler crab U. leptodactyla Rathbun, 1898 was investigated during a one-year period in a tropical mangrove forest in Northeast Brazil (3o 43'S, 38o 32'W). The study specifically addressed factors such as absolute density, sex ratio, population structure and handedness. Eight transects were delimited in a mangrove area of Pacoti River. Monthly, two transects were randomly selected and visited. On each transect, ten 0.25 m2 squares were sampled during low tide periods from September 2003 to August 2004. A total of 1042 crabs was captured, of which 522 were male (50.14%) and 520 were female (49.75%). Only 4 ovigerous females were obtained during the study. There was not significant difference between the mean size of males and females. The overall size frequency distribution was unimodal, with the females being most abundant in the largest size classes, while the males in the smallest. The overall sex ratio (1:0.99) did not differ statistically from 1:1 proportion. The ratio between right-handed and lefthanded males was 1:0.95 and did not differ significantly of the 1:1. The observed average density was 17 individuals/m2 , being widely found on open fields. The unimodal distribution, with juvenile being found year-round, suggests a stable population, with breeding taking place throughout the year, although the low number of ovigerous females collected didn't represent the peak of reproductive activity of U. leptodactyla.