Benthic-Pelagic Linkages in Lakes: Using Stable Isotopes to Quantify Effects of Residential Shoreline Development on Lake Ecosystems

Historically the importance of benthic primary production to the structure and function of lake ecosystems has been underestimated. With increasing recognition of the importance of benthic-pelagic linkages in lakes, researchers recently have demonstrated that benthic production can ‘subsidize’ pelagic food webs. These findings indicate that loss of benthic production may lead to a reduction in the production and stability of pelagic food webs in lakes. This recent line of research has begun to investigate how natural differences in lake morphometry influence the contribution of benthic primary production to lake food webs as a whole, and the implications for lake ecosystems. My project added an innovative component to this line of research by investigating the effects of human activities in the riparian zone of lakes on benthic-pelagic coupling within lakes. Recent research has demonstrated that residential development of lake shorelines degrades littoral habitat, but the food web and ecosystem ramifications of these changes have not been quantified. With support from the Center for Water Science Venture Grant Program, I samples 8 lakes in southeastern Michigan to test the hypotheses that increased residential development of lake shorelines (and associated simplification of littoral zone habitat) reduces the contribution of benthic production to fishes, and essentially shortens the aquatic food chain, thus potentially altering fish species composition, changing food web dynamics, and reducing ecosystem stability. I used stable isotope analysis to test these hypotheses. During the past year I have successfully developed techniques for sample acquisition, preparation, and analysis, and determined carbon and nitrogen isotopic signatures for snails (benthic food web baseline), mussels (pelagic food web baseline), and several fish species . Venture grant funds were insufficient to support processing of all the samples, but results to date demonstrate that we can successfully distinguish benthic and pelagic sources of energy to aquatic food webs in most lakes. Top predators (black bass) and prey fishes (bluegill and pumpkinseed) are highly dependent on benthic production in these lakes, but the relative contribution of benthic primary production to fish production does not appear to vary predictably with residential development levels.