Apple Snail (Pomacea doliodes) and Freshwater Crab (Dilocarcinus dentatus) Population Fluctuations in the Llanos of Venezuela

Abstract

From July through November 1988 and 1989, apple snail (Pomacea doliodes) and freshwater crab (Dilocarcinus dentatus) populations were surveyed in rice plantations and seasonal wetlands (or esteros) in the ilanos of Venezuela to determine seasonal changes in density and size. Rice plantation sites had significantly higher densities and larger snails than did estero sites. Snail density did not differ significantly between months or years. In contrast, the density and size of freshwater crabs varied significantly by month but not between habitats or years: crabs were smaller and in greatest numbers at the beginning of the rainy season, and then declined in density but increased in size by November. The sex ratio of D. dentatus was skewed towards females, a ratio which was consistent across habitats and months. Fluctuations in snail and crab density and size are discussed in relation to the effects of wetland flooding regimes on the life history characteristics of these animals.