Population structure and reproductive biology of the fiddler crab Uca inversa (Hoffman, 1874) (Brachyura: Ocypodidae)

The population structure and reproductive biology of Uca inversa (Hoffman) were studied in Mozambique for the first time. Crabs were randomly sampled on monthly basis during low tide periods from January to December 2002 at Costa do Sol mangrove, Maputo Bay, southern Mozambique. A total of 1131 crabs was obtained, of which 518 (45.8%) were males, 322 non-ovigerous females (29.3%) and 281 (24.8%) ovigerous females, respectively. The present population presents non-normal size frequency distributions, with males reaching greater size than females. The overall sex ratio (M:F) (1:0.84) was significantly different from the 1:1 ratio. Ovigerous females were present throughout the year and the embryonic development showed synchrony with the gonadosomatic index, in which females carrying eggs close to hatching were more abundant when the gonadosomatic index reached minimum values in the population. Egg number increases with female size. Juvenile recruitment was also continuous with high proportion of young recruits being recorded in winter, probably due to the high reproductive activity displayed in summer. U. inversa exhibits a rapid embryonic cycle accompanied by a rapid larval development and settlement in the study area.