Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item Ecosystem Impact of Winter Dinoflagellate Blooms in the Choptank River, MD(2016) Millette, Nicole Catherine; Pierson, James; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Heterocapsa rotundata is a dinoflagellate species that is known to form winter blooms in coastal and estuarine systems. Despite evidence that winter H. rotundata blooms are a common occurrence, there is a lack of laboratory and field-based research on the ecology of this species. My goal was to understand the impact these blooms had on the plankton food web and whether the winter blooms influenced the spring ecosystem. A majority of my research was done with water collected from the Choptank River, MD over the course of five winters. I conducted dilution and prey removal experiments to address the importance of top-down control to the formation of winter blooms. These experiments showed that appropriate environmental conditions are necessary for high H. rotundata growth, and that a bloom will not form unless zooplankton grazing pressure is reduced. I also used a combination of laboratory and field experiments to address whether mixotrophy helps H. rotundata bloom in winter, and my work showed that H. rotundata typically dominates winter blooms because they are a mixotrophic species that uses phagotrophy to overcome the light limitation of winter. I used cultures of Eurytemora carolleeae and H. rotundata to test if high H. rotundata abundances benefit E. carolleeae populations. I found that H. rotundata has no effect on E. carolleeae egg production rate or hatching success rate, but that they can increase the survival E. carolleeae nauplii. Ultimately, through the use of historical data and a temperature based E. carolleeae developmental model, I discovered that lower winter temperatures improve the potential for high annual recruitment of anadromous fish larvae hatched in spring in Chesapeake Bay. Winters with below average temperatures reduce the development rate of E. carolleeae nauplii hatched in winter, and H. rotundata blooms are likely to form and that increase the survival of E. carolleeae nauplii. The delayed development and increased survival causes distinct peaks in E. carolleeae populations later in spring, increasing the chance of high E. carolleeae abundance when fish larvae start feeding. Overall, my research has shown the winter temperature and plankton community can influence the spring ecosystem, specifically the survival and recruitment of anadromous fish larvae.Item INTERACTIONS OF VIBRIO CHOLERAE SEROGROUPS O1 AND O139 AND COPEPODS(2005-05-26) Rawlings, Tonya Kafi; Colwell, Rita R; Ruiz, Greg M; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Vibrio cholerae O1 El Tor and O139 Bengal have caused cholera epidemics throughout Bangladesh and elsewhere in the world with a seasonal regularity. This has raised questions about whether clinical presentations of cholera caused by these two epidemic serogroups of V. cholerae reflect similar responses to their aquatic habitat. The association of V. cholerae with plankton has been suggested to be an important factor in transmission of the disease. In this study, differences in resource utilization of copepods and chitin by V. cholerae O1 and O139 were analyzed using laboratory microcosm experiments. When occurring separately, V. cholerae O1 and O139 were able to colonize copepods, including Acartia tonsa and Eurytemora affinis. However, V. cholerae O1 had a higher affinity for colonizing adults of both copepod species, as well as the multiple life stages of E. affinis, than V. cholerae O139. In sympatry, colonization of copepods by V. cholerae O1 and O139 did not result in specific exclusion of one serogroup by the other. Results of this study indicate that cells that are already established may facilitate attachment through new biofilm formation, notably by V. cholerae O139. Soluble chitin, employed as a nutrient source, supported growth of V. cholerae O1 and O139. Growth of both serogroups with the addition of chitin was significantly greater than in river water alone. In competition assays, V. cholerae O139 had a deleterious effect on V. cholerae O1 growth, but not vice versa. Together, these data indicate that V. cholerae O1 and O139 respond differently to copepods as habitat, as well as nutrient resources. Such differences may play a role in cholera epidemics. The spatiotemporal dynamics of V. cholerae in the environment is complex, and understanding what drives cholera outbreaks requires explicit consideration of population responses and interactions of multiple serogroups.