Illinois Natural History Survey - University of Illinois

Effects Of Exotic Species and Human Impacts on Essential Fatty Acid Availability in the Lake Michigan Food Web

Sergiusz Czesny (INHS), John Dettmers (INHS), Konrad Dabrowski (OSU), Jacques Rinchard (OSU)

In Lake Michigan, yellow perch recruitment is substantially lower than it was 15 years ago. Although recruitment success of yellow perch may be related to alewife abundance and affected by maternal traits, other evidence suggests that shifts in zooplankton numbers and taxonomic composition may also affect yellow perch recruitment. These shifts in the amount and type of food available in the food chain may be related to several human-induced activities. Of particular interest are food-web changes that may be occurring due to the presence of exotic invasive species that act as food-web disruptors.

Lake Michigan has been invaded by a number of non-indigenous species. The recent appearances of the spiny water flea Bythotrephes cederstroemi, zebra mussel Dreissena polymorpha, and round goby Neogobius melanostomus have dramatically altered the existing communities and therefore the food-web structure. Two ways in which these species have acted as food-web disruptors include 1) changing the composition of pelagic zooplankton toward smaller cladocerans and copepods and 2) filtering suspended particulates from the water column, thus reducing the available biomass of phytoplankton and increasing water transparency. At the same time, the depletion of stratospheric ozone resulting from airborne pollutants has generated additional concern that damaging intensities of ultraviolet (UV-B) radiation (280-350 nm) are penetrating deeper into freshwaters.

Polyunsaturated fatty acids (PUFA), are especially sensitive to UV radiation, owing to lipid peroxidation and reduced synthesis by algae. Thus, food-web disruptors, coupled with effects of reduced nutrient loading, provide the favorable conditions for increased UV penetration to dramatically alter the concentration of essential fatty acids throughout the food web. Such shifts in food-web structure likely lead to insufficient PUFA content in the fish prey base and can dramatically depress recruitment success of fish larvae, which have high PUFA requirements.

In this project we evaluate the consequences of altered PUFA concentrations in the Lake Michigan food web and their impact on the reproductive success of yellow perch.

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