Date of Award
Ciberowski, J. J. H.
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Burrowing mayflies of the genus Hexagenia are sensitive to conditions of low dissolved oxygen, and their population has been proposed as an ecosystem objective for assessing the recovery from eutrophication of mesotrophic lakes in which they were once abundant. While acute oxygen tolerance limits are known for Hexagenia nymphs, effects of prolonged exposure to sublethal levels of hypoxia have not been previously studied. I conducted 21-day laboratory experiments examining hypoxic stress in relation to different densities (1, 5, 10 and 20 individuals per 70 cm$\sp2),$ and in relation to a range of temperatures ($\sim$4-20$\sp\circ$C) characteristics of their Great Lakes habitat. Increasing density had a significant negative effect on survival in experiments with low overall survivorship. When survivorship was high, the interaction of oxygen stress (2.0-4.3 mg/L (O$\sb2$)) and density significantly influenced survival, but density alone did not. Density was negatively correlated with growth under oxygen stressed conditions in cultures that had high overall survivorship, and positively correlated with growth in cultures that had low survivorship. Survival of nymphs increased with oxygen concentration up to an asymptote at approximately 7-8 mg/L. Survivorship increased with temperature up to an asymptote at approximately 9.5$\sp\circ$C. Higher temperatures aggravated the effects of hypoxia on survivorship. Oxygen and temperature together explained 89% of the variability in survivorship and 71% of the variability in growth among experiments. Within experiment, larger nymphs generally had higher survivorship than smaller nymphs, and this trend exhibited a slight positive correlation with temperature. My data predict a gradual increase for survivorship and total biomass of nymphs in western Lake Erie. Combined with in situ monitoring of oxygen and temperature conditions, these results should enable us to anticipate the time to reestablishment of the Hexagenia population in mesotrophic habitats. (Abstract shortened by UMI.)Dept. of Biological Sciences. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1994 .W56. Source: Masters Abstracts International, Volume: 34-02, page: 0656. Adviser: Jan J. H. Ciborowski. Thesis (M.Sc.)--University of Windsor (Canada), 1994.
Winter, Andreas Gustav., "Influence of oxygen stress, temperature and density on the growth and survivorship of Hexagenia nymphs (Ephemeroptera: Ephemeridae)." (1994). Electronic Theses and Dissertations. 2440.