Dr. Orlando Sarnelle, Michigan State University

Seminar Abstract: Dr. Sarnelle will summarize findings of his research group that address the complex interaction between invading dreissenid mussels and the toxigenic phytoplankter, Microcystis aeruginosa. His group has conducted a series of field experiments and multi-lake surveys to understand the factors that drive variation in the strength and direction of mussel grazing on M. aeruginosa. To date, they have found that mussel invasion causes an increase in the biomass of M. aeruginosa and an increase in concentrations of the toxin, microcystin, in lakes with total phosphorus concentrations (TP) less than ~20 µg L^-1. At higher TP, survey data and results from a field experiment in 2007 show no effect of mussels on this species. Monitoring of surface waters at the shoreline (the primary point of human recreational contact) also indicate that oligotrophic lakes (TP ~ 10 µg L^-1) with mussels can have episodic levels of microcystin that are as high or higher than in highly eutrophic lakes.

Mechanistic work by Sarnelle's group has shown that there is large intraspecific variation in the grazing vulnerability and intrinsic growth rate of M. aeruginosa within and across lakes, and that some of this variability is genetically based. This may provide one means of explaining variation in mussel effects across systems. Most recently, experimental evidence suggests complex effects of nitrogen (N) availability on the growth of M. aeruginosa and the per capita production of microcystin (toxin quota). Moderate reduction in nitrate levels resulting from P addition led to an increase in M. aeruginosa biomass but a decrease in toxin quota, while severe nitrate reduction led to declines in both biomass and quota.

Research Interests: Dr. Sarnelle is a limnologist and ecologist with relatively broad interests. A major theme in his research has been to understand the roles that interactions among aquatic populations (from phytoplankton to fish) play in population and community dynamics within lakes. He also examines how these interactions impact the overall functioning of aquatic ecosystems. Sarnelle's research group has been working on understanding the complex interaction between invading dreissenid mussels and the harmful phytoplankter, Microcystis aeruginosa. They are currently trying to figure out why zebra mussels seem to have opposite effects on this species in different freshwater systems. Sarnelle also maintains an long-standing interest in herbivore-phytoplankton interactions, with an emphasis on harmful cyanobacteria. The approach that he takes to research questions relies very heavily on field experimentation, and he is very interested in assessing how well such experiments inform us about processes in nature. Recently, Sarnelle's interests have been moving in the general direction of investigating the consequences of trait variation and adaptive evolution within species as drivers of variation in the strength and direction of species interactions in nature.

Host: Dr. David Strayer