Salinity effects on survival and life history of two freshwatercladocerans (Daphnia magna and Daphnia longispina)

Abstract

Salinity is a serious threat to freshwater ecosystems, particularly those near coastal areas. An increase in salinity producesdrastic changes in community structure of freshwaters, sometimes in an irreversible fashion. Thus, freshwater species must copewith salinity stress in a manner proportional to their degree of tolerance. Bearing this in mind, we studied the acute and chroniceffects of different salinity concentrations in two species of cladocerans: Daphnia magna Straus, a standard test organism, andDaphnia longispina O. F. Müller, an autochthonous species. Salinity experiments were based on successive dilutions of a stocksolution of NaCl in a synthetic medium. The results showed that D. magna is more tolerant than D. longispina, both in acute(EC50 5.9 and 2.9 g/L, respectively) and chronic (EC50 5.0 and 2.2 g/L, correspondingly) exposures. In the chronic exposure,salinity caused a significant reduction in fecundity and a developmental delay (increase in age at first reproduction), as well asa decrease in the growth rate of daphnids. However, these effects were mainly observed at salinity concentrations where mortalityoccurred.