Yearly reproductive activity of Limnoperna fortunei (Bivalvia) as inferred from the occurrence of its larvae in the plankton of the lower Paraná river and the Río de la Plata estuary (Argentina)

Abstract

Densities of planktonic larvae of the Asian freshwater invasive pest bivalve Limnoperna fortunei (Dunker) were monitored weekly between 19 September 1997 and 22 January 1999 at two sites: the Parana de las Palmas river, ca. 130 km north of Buenos Aires (33°57.5′ S, 59°12.5′ W), and a coastal station on the Rio de la Plata estuary, in Buenos Aires (34°33.5′ S, 58°24.5′ W). Very variable but generally high (up to 25 000–35 000 ind. m−3) concentrations were recorded at both sites in September 1997-April 1998, and again in August 1998–January 1999, suggesting continuous reproduction during these months. In May through July 1998 larval densities were generally below 100-200 ind. m−3. The threshold temperature level associated with the onset and termination of reproduction was ca. 16–17 °C. With the exception of August-September 1998, when Rio de la Plata temperatures were below 16.7 °C and larval concentrations less than 1000 ind. m−3, whereas those of the Parana were above 16.7 °C, with 1300–13 000 larvae m−3, coupling between the two sites investigated was generally good. Since its invasion in Argentina around 1990, L. fortunei has rapidly become a major nuisance for industrial and power plants located along the lower Parana and Rio de la Plata. The fact that the mollusc produces larvae during 9 months per year greatly hinders its control.