Life cycle and production of the exotic snail physa venustula (pulmonata: Physidae) in the napostá grande stream, southern pampas, Argentina

Abstract

The life cycle of Physa venustula Gould, 1848 (Physidae) in Napostá Grande stream is semelparous and subannual, with two or three poorly defined cohorts per year. Oviposition and recruitment are almost continuous. Juvenile mortality is high up to the length of 3.5 mm and decreases in subadults and adults. Density fluctuations are tied to hydrodynamic conditions and drift events rather than to reproductive activity. Density and biomass in vegetated bottoms were higher than in sandy-mud ones. Annual somatic production estimated by the size-frequency method was low (0.095 g(dry weight).m−2) and turnover rate high (8.10 yr−1) when compared to those of other Physidae. © 2001, Copyright Taylor & Francis Group, LLC.