INTERACTIONS OF PHYTOPLANKTERS CULTURED FROM A POLLUTED SALINE LAKE,ONONDAGA LAKE,NEW YORK1,2,3

Two-membered cultures of 3 phytoplankters isolated from Onondaga Lake, grown in defined media under laboratory conditions, were analyzed by electronic particle counts and statistical methods to determine antagonistic, neutral, or stimulatory relationships. Over the range studied (exponential phase of growth, nutrients not limiting), growth of Staurastrum paradoxum is markedly reduced in the presence of Chlamydomonas sp. Growth of Chlamydomonas is not affected by presence of Staurastrum. The initial concentration of Staurastrum has an effect on its subsequent growth. The initial concentration of Chlamydomonas does not have an effect on its subsequent growth nor that of Staurastrum. These effects are not mediated by a filterable factor (unless highly labile) or by competition for a nutrient. They resemble, and perhaps describe, fluctuations of these species in the lake.