Global change is altering the community composition, variability, and behavior of organisms in a diverse suite of ecosystems. Because of climate change and eutrophication, freshwater lakes and reservoirs are experiencing an increase in low dissolved oxygen concentrations (hypoxia) in their bottom waters (hypolimnion), which can disrupt ecological communities. Zooplankton, important aquatic organisms for regulating water quality and food webs, are one group of organisms affected by hypoxia since zooplankton need oxygen to respire.
My research shows that hypoxia may disrupt zooplankton behavior and increase the variability of zooplankton communities. Zooplankton ubiquitously exhibit diel vertical migration, where the majority of the population resides in the hypolimnion during the daytime to escape predation from fish and damage from ultraviolet radiation. At night, many zooplankton ascend to the surface waters to feed on phytoplankton, when there is decreased risk of predation and radiation.
My results from intensive 24-hour sampling campaigns suggest that hypolimnetic hypoxia may alter zooplankton migration, biomass, and behavior, which may in turn exacerbate water quality degradation due to the critical role zooplankton play in freshwater ecosystems. In addition, field surveys in four reservoirs over three years revealed that hypoxia may increase the variability of zooplankton communities compared to oxic conditions. Consequently, as lakes and reservoirs experience increased extent and duration of hypoxia in the future, it is critical to understand how more variable zooplankton communities alter freshwater ecosystem functioning. / Ph. D. / The globalization and extensive use of habitats by humans has created stress on other organisms in many ecosystems; the interactions, migration patterns, and composition of species have been altered globally because of humans. In freshwater lakes and reservoirs, warmer water temperatures and increased nutrient pollution have resulted in decreased oxygen concentrations in many waterbodies. Decreased oxygen concentrations can affect the organisms living in these environments that need oxygen to survive, which can disrupt the water quality and function of the ecosystem. Zooplankton, or animal plankton or animal drifters, are one group of organisms affected by low oxygen conditions. Zooplankton play an important role in aquatic ecosystems. Zooplankton eat phytoplankton (at the base of the food chain) and are consumed by fish; therefore, any changes to zooplankton populations from low oxygen concentrations can affect water quality and fisheries. My research shows that low oxygen concentrations affect the migration patterns of zooplankton. Zooplankton generally migrate vertically in the water column of a lake and reservoir over each 24-hour period to optimize their proximity to phytoplankton (their food source), while minimizing their chance of being eaten by fish. I found that low oxygen concentrations disrupt this cycle; zooplankton largely do not vertically migrate under low oxygen concentrations. My results from intensive 24-hour sampling campaigns and sampling over multiple summer periods suggest that low oxygen concentrations disrupt zooplankton migration and behavior, which may exacerbate water quality issues in lakes and reservoirs.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/83574 |
| Date | 19 June 2018 |
| Creators | Doubek, Jonathan Patrick |
| Contributors | Biological Sciences, Carey, Cayelan C., Brown, Bryan L., Little, John C., Belden, Lisa K. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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