Date of Award

Spring 2012

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biological Sciences

Program/Concentration

Biology

Committee Director

Mark J. Butler, IV

Committee Member

Holly D. Gaff

Committee Member

Jeffrey D. Shields

Call Number for Print

Special Collections LD4331.B46 T54 2012

Abstract

The blue crab Callinectes sapidus occurs along the Atlantic and Gulf coasts of the United States, and in high salinity regions, they are subject to lethal infection by the parasitic dinoflagellate Hematodinium. In Virginia's seaside estuaries, the prevalence of Hematodinium infection of C. sapidus can sometimes exceed 50%, threatening the commercial fishery for this species. Indeed, other commercially important crustacean fisheries have approached collapse due to Hematodinium infections. Most studies of this host-parasite interaction have focused on epidemiology, host-pathogen dynamics, and pathogen transmission, and little is known about the impact of the parasite on host behavior and population dynamics. In this study, I examined the effects of Hematodinium infection on blue crab activity, mortality from predation, and habitat use. I used an experimental raceway to test for differences in movement between infected and uninfected adult crabs, and found that parasitism by Hematodinium had no significant effect on crab mobility regardless of the level of infection. However, in a separate laboratory experiment where crabs could range more freely among habitats, I discovered that infected juvenile crabs were significantly less active than uninfected crabs, and that crabs preferred seagrass over sand or oyster habitat regardless of infection status. I also tethered infected and uninfected adult crabs in seaside bays of the Virginia Eastern Shore to estimate relative rates of predatory mortality, and found that infected crabs suffered significantly higher predation than uninfected crabs. Similarly, infected juvenile crabs experienced significantly higher predation than uninfected conspecifics in laboratory experiments where they were exposed to an adult crab predator. Those same laboratory experiments revealed that uninfected juvenile crabs buried more frequently and reduced their movement in response to chemical cues produced by adult crab predators, whereas infected crabs did not. These results indicate that Hematodinium infections can alter natural predation rates and crab behavior in ways that may change disease dynamics. Specifically, the reduced mobility and higher predation on infected hosts may limit the spread of Hematodinium in blue crab populations, especially among juveniles.

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DOI

10.25777/mgwt-ws93

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