Intraspecific variation in lake Daphnia affects response of algae and a cyanotoxin to fertilization

Session: Finger Lakes Water Quality (2)

Michael Chislock, The College at Brockport, State University of New York, [email protected]
Lillian Denecke, SUNY-Brockport, [email protected]
Maria Sepulveda, Purdue University, [email protected]
Orlando Sarnelle, Michigan State University, [email protected]
Alan Wilson, Auburn University, Fisheries,, [email protected]

Abstract

Eutrophication is perhaps the most widespread of all human perturbations. Humans have artificially enhanced the productivity of terrestrial and aquatic ecosystems on a global scale by increasing nutrient loading (i.e., cultural eutrophication). While the consequences of cultural eutrophication are well-known (e.g., toxic algae), the potential role of adaptation by organisms in modulating the responses of ecological systems to such perturbations is unknown. We tested the hypothesis that adaptation by a generalist herbivore in lakes (Daphnia pulicaria) to toxic cyanobacteria mediates the response of phytoplankton to nutrient enrichment. We conducted large-scale field experiments where we manipulated nutrients (ambient; fertilized) and Daphnia (no Daphnia; cyanobacterial-sensitive Daphnia; cyanobacterial-tolerant Daphnia) using a fully factorial design. Sensitive and tolerant genotypes had comparable effects on algal biomass under ambient nutrients. In contrast, with fertilization tolerant genotypes resulted in a greater than 80% reduction in algal biomass versus no effect of sensitive genotypes, relative to the no Daphnia control. The interactive effects of fertilization and Daphnia traits were mediated by the positive response of the toxic cyanobacterium Cylindrospermopsis raciborskii and an associated cyanotoxin (saxitoxin) to nutrient enrichment. Thus, the response of lakes to enrichment may depend not only on zooplankton community composition but also grazer evolutionary history.