Hypoxia as a Mediator of Food Web Interactions and Energy Flow in Reservoir Ecosystems

Hypoxia as a mediator of food web interactions and energy flow in reservoir ecosystems

 

Kathryn J. Lang¹, Kevin Pangle², Joseph D. Conroy³, Senaka Goonewardena¹, and Stuart Ludsin¹

¹ The Ohio State University, Aquatic Ecology Laboratory, Dept. of Evolution, Ecology, and Organismal Biology, 232 Research Center, 1314 Kinnear Rd., Columbus, OH 43212   

² Central Michigan University, Dept. of Biology, Brooks Hall 194, Mt. Pleasant, MI 48859

³ Ohio Department of Natural Resources, Division of Wildlife, Inland Fisheries Research Unit, 10517 Canal Road, SE, Hebron, OH 43025

            Hypoxia has emerged as a prominent research and management issue in freshwater and marine ecosystems worldwide, primarily owing to cultural eutrophication.  Our understanding of hypoxia’s impacts on aquatic food webs, particularly pelagic ones, is limited, however.  Herein, we explore how hypoxia can influence reservoir food web interactions involving age-0 fishes (e.g., gizzard shad Dorosoma cepedianum; crappies Pomoxis spp.; bluegill sunfish Lepomis macrochirus), the phantom midge (Chaoborus punctipennis), and their shared mesozooplankton prey.  From sampling with fishery acoustics, midwater trawling, and zooplankton pumping during day and night in Hoover Reservoir, Ohio before, during, and after the hypoxic period in 2011, we learned that hypoxia-driven disruption of the diel vertical migration (DVM) behavior in both planktivore types caused high overlap with mesozooplankton prey in the oxygenated epilimnion during the hypoxic period.  Further, Chaoborus began to feed during the day (not just the night) in the presence of hypoxia and its consumption of mesozooplankton taxa of importance to fish increased.  Using this information, in conjunction with diet overlap and prey size- and taxa-selectivity data for Chaoborus and fish, we discuss the potential for hypoxia to regulate the foraging and growth environment for age-0 reservoir fishes via altered energy flow through the food web. 

Key words: anoxia, reservoirs, predation, planktivory, dead zone, hydroacoustics