Restocking Ucides cordatus (Decapoda: Ocypodidae): interespecific associations as a limiting factor to the survival of released recruits

Abstract

Simulations in the laboratory were used to investigate whether survivorship rates of Ucides cordatus youngsters produced in the laboratory are significantly affected by other crab species after their release in natural environments. Furthermore, it was investigated whether the release of first instar juveniles instead of megalopae would reduce the mortality related to interspecific predation. A preliminary estimate of the crab community structure in the target area of a restocking program was undertaken and indicated a great dominance of fiddler crabs (Uca spp). Based on this information, experiments were conducted to assess the ecological relationship between Ucides cordatus megalopae and first instar juveniles and fiddler crabs of different size classes in the presence of mangrove sediment, simulating natural conditions, as well as in the absence of any kind of refuge. It was observed that fiddler crabs not only compete with, and prey on U. cordatus youngsters, both as megalopae and juveniles. Furthermore, it was observed that the predation behavior of fiddler crabs is exercised only by individuals with carapaces wider than 0.5 cm. The results of the assay simulating natural conditions showed that, even when sediment was provided as a refuge, the same pattern was observed, with survivorship rates significantly lower in the presence of Uca crabs.