Ecological aspects of the populations of the crabDotilla fenestrata(Hilgendorf, 1869) (Brachyura: Ocypodidae), in the tidal flats of Inhaca Island (Mozambique)

The population of Dotilla fenestrata of Inhaca island was studied, on the basis of fortnightly sampling during a period of four months. At three tidal levels and in two collecting transects, crabs were counted, sexed and measured, and eggs counted. Results indicate a preference of the crabs for the lower level, although there is a high degree of variability of abundance in relation to the unstable profiles of the sand banks. Diameter of burrow entrance is strongly correlated to crab size, which may prevent predation by larger animals. The rhythm of emergence was studied, comparing neap to spring tides. Results indicate that crabs are more rapid in initiating surface activity, mainly feeding, during neap tides, and during spring tides the delay is related to tide level. Feeding rhythm is independent of animal size, but weight of feeding pellets produced increases with crab size. Sponging rhythm decreases with crab size, which suggests a more efficient water intake by larger animals.