Population structure and breeding season of the hermit crab Diogenes brevirostris Stimpson, 1858 (Decapoda, Anomura, Diogenidae) from southern Mozambique

In this study the population dynamics of the diogenid hermit crab Diogenes brevirostris is evaluated focusing on size structure, sex ratio and breeding season. Crabs were randomly taken on a monthly basis from January to December 2003 at Costa do Sol, Maputo Bay, southern Mozambique. A total of 622 crabs was obtained of which 290 were males (46.6%), 170 were non-ovigerous females (27.3%) and 162 were ovigerous females (26.1%). The overall size frequency distribution was unimodal for males, non-ovigerous females and ovigerous females. The overall sex ratio (1:1.15) differed from the expected 1: 1 ratio. Sexual dimorphism was evidenced by the larger size attained by males in relation to both ovigerous and non-ovigerous females. Breeding took place year-round with three peaks of spawning (March, August and December). Despite the high reproductive activity, young recruits were scarce in the population. The present results suggest that the study area is suitable for reproduction and growth whereas recruitment may take place in different areas from that occupied by the adults.