Abstract
During quantitative samples of invertebrate fauna in two lakes in the Rio Doce State Park (Marliéria, MG) I found some individuals of the introduced aquatic snail Melanoides tuberculata. It was most abundant in areas with high human activity, where the original vegetation was removed from the shallow areas near the margin. Population structure inferred by size-class data suggests that the most impacted area was invaded first and that these snails maintain a viable population in Dom Helvécio lake. Potential spread of the snail in this lake system is tentatively related to the characteristics of the bank vegetation and I presume that the not yet invaded Carioca lake has better conditions for an exponential growth of this species.