Comparative population biology of Uca rapax (Smith, 1870) (Brachyura, Ocypodidae) from two subtropical mangrove habitats on the Brazilian coast

Abstract

The structure of two populations of the fiddler crab Uca rapax in two subtropical mangrove habitats near Ubatuba, State of São Paulo, Brazil were compared. The size–frequency distribution, sex ratio, and recruitment were evaluated. Sampling was performed monthly from April 2001 to March 2002 in the Itamambuca and Ubatumirim habitats. Crabs were caught manually for 15 min by two collectors during low tide. The carapace width of each crab was measured with a digital caliper, and the sex and ovigerous state were recorded. The median size of the carapace width of males was greater than that of females at both sites (P<0.05). The median size of the crabs from Itamambuca was larger than at Ubatumirim (P<0.05). Only 28 ovigerous females were obtained from both mangroves, which suggested that females might remain in their burrows during the incubation period. The highest recruitment pulse occurred in winter for both populations, probably as a consequence of high reproductive activity during summer. The sex ratio in the size classes showed an anomalous pattern, with a higher frequency of females in the intermediate size classes. This may be related to a greater energy requirement for reproduction in females, thus delaying growth. The variable environmental conditions to which Uca rapax populations are subject appear to act directly or indirectly on the population, causing variations in growth and reproductive processes in the different populations investigated here.

Keywords:

• Decapoda
• Brachyura
• Uca rapax
• population biology

Acknowledgements

The authors acknowledge the Fundação de Amparo à Pesquisa do Estado de São Paulo for a fellowship to the first author (#01/01810‐9) and support for transportation (#98/3134‐6); and our colleagues at NEBECC for their help during field and laboratory activities. This work was carried out according to state and federal laws concerning wild animal sampling.

Notes

Ita, Itamambuca; Uba, Ubatumirim.

Lowercase letters correspond to comparisons within the same environmental factor among seasons of the year; uppercase letters correspond to comparisons within the same environmental factor and season but between sites. Values with at least one letter in common did not differ statistically (ANOVA; α = 0.05).