Effects of PCB on interspecific competition in natural and gnotobiotic phytoplankton communities in continuous and batch cultures

The toxicity of polychlorinated biphenyls (PCB) to the diatom Thalassiosira pseudonana (formerly Cyclotella nana), grown in pure and mixed cultures, was greatest when in competition with other species. Continuous cultures were superior to batch cultures for studying competitive interactions, and PCB caused greater alteration of species composition in continuous cultures than it did in batch cultures. Natural phytoplankton communities from Vineyard Sound, maintained in continuous culture, responded to PCB stress the same as did gnotobiotic communities, with T. pseudonana showing similar responses in both communities. A PCB concentration of 0.1 μg/liter (0.1 part per billion), a level not uncommon in natural waters, did not affect algal growth in pure cultures but caused substantial disruption of continuous culture communities. The possible impact of PCB pollution on natural phytoplankton communities is discussed.