The Recurrent Coastal Plume in Lake Michigan:
A Critical Event for Copepod Reproduction and Recruitment

H. Vanderploeg and M. Bundy (Principal Investigators)
with W.C. Kerfoot (subawardee)

This project is part of a larger multidisciplinary effort to investigate the influence of the Lake Michigan Recurrent Coastal Plume (LMRCP) on trophic energy transfer during the critical winter-spring transition period in Lake Michigan. The study will increase understanding of the impacts of large-scale episodic events on ecological processes in large lakes and marine coastal areas in general, and in the Laurentian Great Lakes in particular. Altered levels of light, nutrients, and physical mixing in the LMRCP may affect the dynamics of secondary production in the region by changing the composition, production rates, and fate of primary production in the plume relative to offshore waters. The purpose of this proposal is to address the general hypothesis: Large episodic events, such as the LMRCP, change mesezooplanktonic community structure and production by altering copepod species and life-stage distributions and trophic interactions.
Field observations, process studies, and laboratory investigations will be combined to evaluate physical and biotic effects of the LMRCP on the mesozooplankton community. Biweekly "monitoring" of nutrients, physical variables, phytoplankton, MFW organisms, and mesozooplankton at the primary study site will serve to put the LMRCP in perspective with ongoing changes in the plankton and other events, and will help evaluate its significance to the Lake as a whole. Spatial distribution of mesozooplankton and chlorophyll relative to plume boundaries will be mapped out using a plankton survey system (PSS), which consists of an optical plankton counter, CTD, and fluorometer towed on a V-fin in an undulating mode. Field and laboratory experiments will examine both community and species-specific grazing rates on natural seston and mixtures of cultured prey representing key prey types. Egg production rates and nauplii survival will provide a means of assessing the influences of recent feeding history on copepod secondary production. Because only adult copepods overwinter, abundances of juveniles will provide an estimate of new recruits into the population, except for those species that produce resting eggs. Resting egg abundance will be determined in the water column, sediments, and sediment traps. The response of mesozooplankton to large scale episodic events during the winter-spring period in the Great Lakes and other similar aquatic systems is important at the ecosystem level because these populations play a pivotal role in energy transfers and nutrient transformations that occur throughout the rest of the year.