Condition index and growth rates of field caged Corbicula fluminea (Bivalvia) as biomarkers of pollution gradients in the Paraná river delta (Argentina).

CATALDO DANIEL; BOLTOVSKOY DEMETRIO; STRIPEIKIS JORGE; POSE MONICA

AQUATIC ECOSYSTEM HEALTH AND MANAGEMENT

TAYLOR & FRANCIS INC

Lugar: New York; Año: 2001 vol. 4 p. 187 - 201

1463-4988

In 1995-1996, Corbicula fluminea was collected at monthly intervals at two sites in the delta of the lower Paraná river (Argentina): at the confluence of the San Antonio and Vinculación rivers (SA site), and the Paraná de las Palmas river, close to its outlet into the Río de la Plata estuary (PP site). The SA site is located in the vicinity of strong sources of industrial and sewage effluents, whereas the more remote PP sampling location is considerably less polluted. Growth rates of caged individuals at the two sites were also monitored during the same period, and Cu, Cd, Pb and Zn were measured monthly in the water and in tissue of animals. Throughout the year concentrations of all metals in water, as well as Pb and Zn in tissue, varied irregularly and their levels at the two sites were roughly similar; on the other hand, Cu and Cd in tissue of animals from SA were consistently and significantly higher than in those from PP. Changes in the size-frequency of clams from PP throughout the period surveyed clearly indicated a highly structured population with a single well defined reproduction period in October-November. In contrast, shell lengths at SA changed very little throughout the 13-months period, with over 88% of the clams varying between 18 and 20 mm in length; no discernible cohorts were recorded. Growth rates of caged clams were very significantly lower at SA than at PP, with the latter yielding comparable values to those obtained from PP cohort analysis data. Highest growth rates (around 10 mm) were attained by the smallest (ca. 7-8 mm) clams reared in PP waters, whereas 23-25 mm organisms maintained in SA waters grew only 2-3 mm in the same period. Of the 57 animals which survived throughout the caging experiment, those below 10 mm at the outset increased, on average, 8.2 mm in length after 13 months, whereas clams >10 mm grew only 4.2 mm. The condition index (i.e., dry tissue weight divided by shell length) of clams from SA was consistently ca. 50% lower than that of clams from PP. It is concluded that delayed growth, poorer condition index, and the abnormal population structure at SA are due to enhanced pollution in this area as compared with PP, and that all three traits constitute a more useful biomarker of environmental stress than chemical analyses of contaminants.