Digitized Honors Theses (2002-2017)

Date of Award

5-2003

Document Type

Undergraduate Thesis

Degree Name

BS

Department

Biology

Faculty Mentor

Jack O'Brien

Advisor(s)

Tim Sherman, Ph.D., Anne Boettcher, Ph.D., Kelly Major, Ph.D.

Abstract

The greater blue crab Callinectes sapidus is important in commercial fisheries along the U.S. eastern seaboard and Gulf of Mexico. This crab species is parasitized by the rhizocephalan barnacle, Loxothylacus texanus, which is restricted to the Gulf of Mexico and adjacent regions including the Atlantic seaboard south of South Carolina. In order to better understand the factors affecting the distribution of L. texanus, this study investigated environmental conditions that influence settlement of the parasite on its crab host as well as levels of parasite infection in crabs from Alabama waters. Environmental parameters examined include the effect of salinity on carapace composition and the role that sediment type and water depth have on settlement. Salinity has an effect on carapace composition. Crabs maintained at 25%0 have higher calcium and lower protein content post-molt than crabs maintained at 5%o. Past research shows that salinity also affects the survival and settlement response of L. texanus larvae. Other environmental factors, including sediment type affect settlement. L. texanus larval settlement was observed to occur more often over mud than sand in both field and lab experiments. There was no difference in settlement in surface water vs. bottom environments. Although we know that abiotic factors can affect settlement, past studies have not Jinked environmental conditions with levels of infection. Blue crab samples taken from two sites along the Alabama Gulf Coast, Pointe aux Pines, AL and Airport Marsh Dauphin Island, AL were tested for infection using a polymerase chain reaction (PCR) based method. This method has been successfully used to amplify a 212 base pair sequence only present in infected tissue. No product is formed in tissue without L. texanus present. Thus far, no samples from our collection sites have tested positive for the parasite. Future experiments will focus on the relative importance of specific factors influencing the settlement of L texanus and continue to examine the distribution patterns of the parasite.

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