MEPS 411:173-188 (2010)  -  doi:10.3354/meps08656

Effects of hypoxia on Mnemiopsis leidyi, ichthyoplankton and copepods: clearance rates and vertical habitat overlap

Sarah E. Kolesar1,2,4,*, Denise L. Breitburg2,5, Jennifer E. Purcell3,6, Mary Beth Decker3,7

1Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, PO Box 38, 1 Williams Street, Solomons, Maryland 20688, USA
2Academy of Natural Sciences Estuarine Research Center, 10545 Mackall Road, St. Leonard, Maryland 20685, USA
3Horn Point Laboratory, University of Maryland Center for Environmental Science, Cambridge, Maryland 21613, USA
4Present address: Oregon Sea Grant, Oregon State University, 307 Ballard Extension Hall, Corvallis, Oregon 97331, USA
5Present address: Smithsonian Environmental Research Center, 647 Contees Wharf Road, Edgewater, Maryland 21037, USA
6Present address: Shannon Point Marine Center, 1900 Shannon Point Road, Anacortes, Washington 98221, USA
7Present address: Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut 06520, USA

ABSTRACT: Differences in predator and prey tolerances to low dissolved oxygen (DO) concentrations influence planktonic food web interactions in seasonally hypoxic environments. We examined low-DO effects on predation by hypoxia-tolerant ctenophores, Mnemiopsis leidyi, on less hypoxia-tolerant ichthyoplankton prey in laboratory experiments. We also examined the relationship between bottom DO concentrations and vertical distributions, and considered potential effects of biotic (predators and competitors) versus abiotic factors (low DO concentration, temperature, salinity, time of day) on vertical habitat overlaps between gelatinous zooplankton and their prey during summer in a Chesapeake Bay subestuary. Laboratory clearance rates of M. leidyi feeding on bay anchovy (Anchoa mitchilli) eggs and yolk sac larvae, and naked goby (Gobiosoma bosc) larvae were as high at low DO (1.5 mg l–1) as at high DO concentrations (7 mg l–1). Multiple years of field sampling at 2 sites revealed that the proportions of motile species in the bottom layer of the water column, especially fish larvae and copepods, increased with increasing bottom DO concentrations during both day and night. Ctenophore densities remained high in the bottom layer even at low DO concentrations. Vertical habitat overlaps among 4 motile predator–prey pairs (M. leidyi–copepods, M. leidyi–naked goby larvae, bay anchovy larvae–copepods, and naked goby larvae–copepods) increased with increasing bottom DO concentrations (1st- or 2nd-order regression models). Vertical overlap between M. leidyi and fish eggs was significantly higher during the day than at night. Statistical models suggest that both bottom DO concentration and scyphomedusan predators influenced M. leidyi–fish egg nighttime and M. leidyi–copepod combined day–night overlaps. Hypoxia influences food web interactions more through altered habitat use and encounter rates than by directly affecting predation. Strong behavioral responses of larval fish and copepods to low bottom DO concentrations may decrease habitat overlap between M. leidyi predators and their prey.

KEY WORDS: Bay anchovy · Naked goby · Fish egg · Fish larva · Ctenophore · Predation · Food web · Chesapeake Bay · Eutrophication · Gelatinous zooplankton

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Cite this article as: Kolesar SE, Breitburg DL, Purcell JE, Decker MB (2010) Effects of hypoxia on Mnemiopsis leidyi, ichthyoplankton and copepods: clearance rates and vertical habitat overlap. Mar Ecol Prog Ser 411:173-188

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