MEPS 205:43-59 (2000)  -  doi:10.3354/meps205043

Effects of bottom-layer hypoxia on abundances and depth distributions of organisms in Patuxent River, Chesapeake Bay

Julie E. Keister1,*, Edward D. Houde1, Denise L. Breitburg2

1University of Maryland, Center for Environmental Science, Chesapeake Biological Laboratory, PO Box 38, Solomons, Maryland 20688, USA 2The Academy of Natural Sciences, Estuarine Research Center, 10545 Mackall Rd, St. Leonard, Maryland 20685, USA
*Present address: Oregon State University, Hatfield Marine Science Center, 2030 S. Marine Science Dr., Newport, Oregon 97365, USA. E-mail:

ABSTRACT: Oxygen depletion, seasonally common in bottom waters of many stratified aquatic systems, may have strong effects on abundances, distributions, and interactions among organisms, and therefore community dynamics. To examine effects of bottom-layer on densities and vertical distributions in a stratified subestuary, fish larvae, their gelatinous predators, and copepod prey were surveyed near-surface, within the pycnocline, and near-bottom in the Patuxent River (Chesapeake Bay) under a range of near-bottom dissolved oxygen (DO) conditions. Overall abundances of fish larvae and copepod nauplii were lower throughout the water column when bottom-layer DO was low (≤2 mg DO l-1). When bottom-layer DO was low (≤2 mg l-1), d larvae were less than one-third of those observed during high (>2 mg l-1) DO conditions, and overall density of copepod nauplii declined by >50%. Depth-distributions of several organisms also were affected by bottom-oxygen depletion: fish larva scyphomedusae, and copepods were much less common near the bottom when bottom-layer DO was low than when it was >2 mg l-1. The ctenophore Mnemiopsis leidyi occurred in high densities at DO as low as 1.3 mg l-1, but was nearly absent results indicate the potential for substantial differences in organism interactions, especially predator-prey relationships, between times of high and low bottom-layer DO.

KEY WORDS: Hypoxia · Chesapeake Bay · Fish larvae · Naked goby · Anchovy · Jellyfish · Vertical distribution · Zooplankton

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