Life cycle and production of the exotic snail Physa venustula (Pulmonata: Physidae) in the Napostá Grande stream, Southern Pampas (Buenos Aires Province, Argentina)

MARTÍN, PABLO

Journal of Freshwater Ecology

Oikos Publishers

Lugar: La Crosse; Año: 2001 vol. 16 p. 93 - 104

Physa venustula Gould, 1848 is an exotic freshwater snail, recently introduced in the Napostá Grande stream, with few scattered records in Argentina. The aim of this study was to investigate its life cycle in this small temperate stream from the semiarid Southern Pampas and to obtain an integrated estimation of its success through the estimation of biomass production. The life cycle of Physa venustula 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. Physa venustula has dispersed rapidly upstream (ca. 10 km.yr-1) along most Napostá Grande drainage basin, but it is not dominant in any part of it. High torrential rain frequency in the drainage basin together with inadequate flow refugia are probably responsible for the unsuitable hydrodynamic conditions for P. venustula in the Napostá Grande stream.