Influence of salinity on metal toxicity to Ulva pertusa

The present study was undertaken to establish the effect of salinity on the toxicity of cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn) to Ulva pertusa, with inhibition of spore release used as the endpoint. The optimal salinity for maximal spore release for U. pertusa was found to be between 20 and 40 psu. Comparisons between toxicity of metals, as measured by EC50, was shown to be in the descending order of Cu>Cd>Pb=Zn, which is similar to the toxicity of metals to algae, in general. When salinity was decreased from 30 to 20 psu, the EC50 values for Cd toxicity to the inhibition of spore release in U. pertusa decreased from 261 to 103 g·L−1, whereas increased salinity from 30 to 40 psu increased the EC50 from 261 to 801 g·L−1. Similarly, EC50 values for Cu toxicity were 52 g·L−1 at 20 psu, 99 g·L−1 at 30 psu, and 225 g·L−1 at 40 psu, and for Zn toxicity were 720 g·L−1, 1,074 g·L−1 and 1,520 g·L−1, at 20, 30 and 40 psu, respectively. In contrast, no salinity dependent change in EC50 values was apparent for Pb, with no significant differences in EC50 values at under the three different salinity regimes. In general, lower salinity (20 psu) induced a significant decrease in percent spore release of U. pertusa as estimated by a decrease in EC50 values, while higher salinity (40 psu) reduced the toxicity of metals as shown by an increase EC50 values. These findings enable one to predict that any additional increase in pollution status would result in a pronounced reduction in the distribution of U. pertusa in brackish and estuarine waters.