AN ANALYSIS OF THE ROLE PLAYED BY GROWTH AND NUTRIENT DYNAMICS REGARDING THE COMPETITIVE SUCCESS OF CLADOPHORA GLOMERATA (L.) KUTZ IN LAKE ONTARIO WITH REFERENCE TO A POTENTIAL COMPETITOR STIGEOCLONIUM TENUE (AGARDH) KUTZ

Cladophora glomerata has dominated the shores of the Lower Great Lakes as a result of recent enhanced eutrophication caused by increased phosphorus loading. Cladophora growth in this system is phosphorus-limited. Bangia atropurpurea is not a potential competitor because it is spatially separated from the Cladophora zone by occupying the splash zone. Ulothrix is a spring and autumn psychrophile and only grows before and after the Cladophora growing season. Stigeoclonium tenue is a potential competitor which outcompetes Cladophora in the laboratory under phosphate-limited conditions. Stigeoclonium exhibits higher phosphate uptake rates and phosphate-limited growth rates. In addition Cladophora requires exogenous thiamine to achieve maximal growth while Stigeoclonium has no such requirement. Cladophora outcompetes other algal species in Lake Ontario (and the Lower Great Lakes) not primarly because of its ability to use phosphate but because of its ability to effectively colonize the littoral zone and function as a perennial. The overwintering akinete resting stage in Cladophora remains attached from year to year, acting as an enormously effective inoculum each spring. For benthic filamentous species to dominate large areas of littoral zone, the overwintering stage is apparently critical to the continual and cumulative spreading and colonization process.