The Effects of Petroleum Hydrocarbons on Algae Can Be Reversed in the Presence of a Primary Consumer.

The ecotoxicological effects of a mixture of petroleum hydrocarbons were tested on densities of two algae, Platymonas helgolandica var. tsingtaoensis and Isochrysis galbana, and of a rotifer, Brachionus plicatilis, by single-species and customized community experiments. Test concentrations ranged from 0 to 100 mg L(-1), while five to seven treatments were assessed in triplicate within 1 month. A significant decrease in densities during single-species toxicity tests were found when concentrations of petroleum hydrocarbons were above 1.0 mg L(-1). However, equilibrium densities of algae in the customized community showed a different pattern, which increased with concentration and reached a peak at 20.0 mg L(-1). The community-based no observed effect concentration (NOEC; 1.0 mg L(-1)) was different from the NOEC derived by single-species toxic tests (0.25 mg L(-1)). This demonstrates that ecotoxicological effects on plankton as part of a community is significantly different from single-species toxicity tests owing to ecological interactions.