Experimental studies on predation and cannibalism of the settlers of Chasmagnathus granulata and Cyrtograpsus angulatus (Brachyura: Grapsidae)

The grapsid crabs Chasmagnathus granulata and Cyrtograpsus angulatus are considered as key species within the benthic communities of estuaries and brackish coastal lagoons in the southwestern Atlantic region. In controlled laboratory experiments, we studied the intensity of interspecific predation as well as intra- and intercohort cannibalism in setllers in relation to refuge availability, predator characteristics (species, size, sex, nutritional state), and the presence or absence of an alternative food source (Artemia nauplii). In both species, the intensity of intracohort cannibalism among recently settled crabs (instars I and II, "settlers") was low, with ca. 5% mortality during 48 h experimental observation periods. Larger juveniles and adults of both species, by contrast, preyed heavily on the settlers. Predation was significantly reduced when refuges were available for the settlers. Hunger of the predators enhanced in general the predation rate. In the presence of alternative food, the consumption of settlers was significantly reduced. In C. granulata, adult females ate more settlers than the males, probably as a consequence of differences in the morphometric traits of their chelae. Cannibalism and predation by juvenile and adult crabs may play an important role in the regulation of recruitment success for both species and hence, in the structure of estuarine benthic communities.