Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


Linda C. Schaffner

Committee Member

J. Emmett Duffy


Community models predict the effects of stress on community structure and processes. I tested the Menge and Sutherland 1987 model in an estuarine epifaunal community experiencing low oxygen stress, termed hypoxia. Epifauna, animals living on the surfaces of substrates, are ecologically important in many estuaries where hypoxia occurs, yet little is known about the effects of hypoxia on these communities. Epifauna formed dense communities in the York River, a tributary of the Chesapeake Bay, USA, despite frequent hypoxia. Abundance and species composition was similar in two areas of the river, even though the downstream study area often experienced lower oxygen concentrations during hypoxic episodes than the upstream study area. Many dominant species exposed to high and low oxygen in the laboratory had a median lethal time (LT50) in hypoxia greater than the duration of typical hypoxic episodes in the York River, suggesting that hypoxia may cause little mortality for many species in this system. Predation by a variety of taxa decreased during hypoxia in the laboratory, because many mobile predators had higher mortality than sessile prey, and because predation rates decreased. Peak recruitment of dominant taxa, and of total epifauna, in the York River occurred during neap tides in the downstream study area, coinciding with the lowest oxygen concentrations. In the laboratory, low oxygen decreased recruitment of dominant taxa, but some recruitment continued in hypoxia for most taxa, indicating that larvae of dominant epifauna are tolerant of hypoxia. Larval tolerance of hypoxia may allow communities to persist even though the recruitment season of many epifaunal species coincides with the peak season of hypoxia. These findings supported some predictions of the consumer stress model, but not all. as predicted, when stress increased, the importance of disturbance for determining community structure increased, while the importance of predation decreased. Unlike predictions, stress changed recruitment rates in the laboratory. There were few effects of stress on abundance and diversity, possibly because in this system hypoxia is mild, brief, and because the species in this community can tolerate stress, colonize disturbed areas quickly, and grow quickly enough to complete life-cycles between hypoxic episodes.



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