The Cause of Cladophora's Resurgence

Abstract

This presentation describes the possible causes of the observed resurgence of the green algae Cladophora within Lake Ontario. A resurgence of eutrophication of the nearshore zone is also occurring without significant changes of point source phosphorous loads. There are signs of cultural eutrophication of nearshore Lake Ontario but there is no evidence of increased phosphorous loading from external sources. The apparent contradiction can be explained through the invasion of the Dreissena mussel which may be changing Lake Ontario’s internal nutrient cycle. A Dreissena-induced nearshore shunt changes the composition and cycling of particulate matter to facilitate nearshore eutrophication. The resurgence of the macro algae Cladophora is related to increased substratum availability, increased water clarity, and changes of the P recycling system associated with the establishment of dense colonies of Dreissena. If the nearshore phosphorous shunt exists then there will be higher SRP concentrations above Dreissena beds. We hypothesize that the samples collected on top of Dreissena mussel beds will have higher concentrations of SRP than over mussel-free substrate. The use of the modified Hesslein Sampler will be able to provide evidence as to whether the metabolic waste products of Dreissena mussels are sufficient enough to produce sever blooms of Cladophora.