Large rivers have not been well-studied because of the difficulty and hazards associated with sampling. In addition, standard sampling techniques used on smaller rivers have not been shown to be effective in adequately characterizing these complex and transient systems. This project will address the functioning of large river ecosystems. The PIs and their undergraduate assistants will construct a set of "potamocorrals" in order to perform empirical investigations on the St. Lawrence River. Large-scale, in situ field experiments involving large river plankton are currently beyond the capabilities of aquatic scientists. These investigators intend to test food web and ecosystem metabolism hypotheses that relate to our general theoretical understanding of large rivers as heterotrophic systems. Specific experiments will consider: 1) the ecological effects of two exotic mussel species on plankton food webs; 2) the effects of differing levels of phytoplankton on ecosystem metabolism; and 3) the effects of mussel planktivory on the growth of planktivorous larval fish. In this latter experiment, the investigators hypothesize that dreissenid mussels are a factor in the decline of bass and walleye in the St. Lawrence through competitive planktivory.
