When bugs are hard to find?

Nymphs of burrowing mayflies (Hexagenia spp.) are a high quality food for many ecologically and environmentally important fishes. However, habitat alteration by Dreissena (zebra and quagga mussels) likely affects habitat choice and availability of mayflies to fish. Behavioral studies show that mayflies chose structured habitat provided by Dreissena clusters over bare sediment; most likely as protection from predation. In laboratory experiments, the effect of Dreissena-covered sediments on fish consumption was that mayflies derived protection from predation by round gobies and yellow perch. However, this occurred only when turbidity was held at a level similar to that observed in western Lake Erie. We mapped mayfly and Dreissena distributions in western Lake Erie and found that over 60% of the sites with Dreissena have at least 100 mayflies/m², suggesting that Dreissena do not inhibit the presence of mayflies in western Lake Erie. Further, on a small spatial scale, Dreissena colonized habitat is preferred by mayflies. Overall, this spatial association lowers the availability of mayflies to fish in turbid conditions. Therefore, the effect of Dreissena on energy transfer of mayflies to fish may be either neutral or negative but no evidence was found of positive effects on energy transfer from dreissenid mussels.