Ryan Carnegie

Date of Award

12-2000

Level of Access Assigned by Author

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Marine Biology

Advisor

Bruce Barber

Second Committee Member

Dan Distel

Third Committee Member

Steve Fegley

Abstract

Health management efforts in Maine related to the flat oyster (Ostrea edulis) parasite Bonamia ostreae are limited by a lack of knowledge of the parasite’s distribution and impact in both wild and cultured populations. This information would be more readily obtainable with improved diagnostic tools. The objectives of this dissertation were to design sensitive and specific DNA probes for detection of B. ostreae; to assess the prevalence and intensity of parasite infections in wild oyster populations in Maine; and to evaluate growth and mortality of cultured oysters in the Damariscotta River, where B. ostreae is enzootic. A polymerase chain reaction (PCR) assay, designed for sensitive in vitro detection of Bonamia ostreae and evaluated against a standard histocytological technique, was positive for B. ostreae in all (100%) “heavily” and “moderately” infected oysters, most (73.3%) “lightly” and “scarcely” infected oysters, and many (37.9%) of the oysters in which the parasite was undetected. No PCR amplification occurred when control (uninfected) oysters were used. A fluorescent hybridization assay designed for in situ detection of B. osfreae in thin sections resulted in specific probe binding to B. osfreae rDNA. Controls using mismatch oligonucleotides confirmed the specificity of this assay. B. osfreae was regularly detected at low prevalences and intensities in one (Gun Point Creek) but not three other (Spinney Creek, Linekin Bay, Blue Hill Salt Pond) wild oyster populations. Growth and mortality of hatchery-produced oysters were greater at an upriver (Little Point) site than at a downriver (Lowes Cove) site on the Damariscotta River. These differences were related to the greater variation in temperature and salinity occurring at the Little Point site. Bonamia osfreae was detected in only one oyster. The results of this study have greatly increased our ability to detect Bonamia osfreae in flat oysters, which will lead to improved management options for growers. There are locations where B. osfreae is not detectable. Under the right environmental conditions, flat oysters can be grown to market size in less than three years. The molecular techniques developed will be useful for future determination of the life cycle of B. osfreae.

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