Date of Award

Spring 5-3-2024

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Animal Sciences

Advisor

Suzanne Ishaq

Second Committee Member

Jennifer J. Perry

Third Committee Member

Timothy Bowden

Abstract

Placopecten magellanicus, also known as the Atlantic deep-sea scallop, is a valuable marine species on North America's northeastern coast. Although adult scallops can be successfully bred in hatcheries, a perplexing and destructive event takes place during the last two weeks of larval development: a sudden and severe mortality event that causes a drastic decline in populations, with some reports suggesting that survival from egg to competent larva can sometimes be reduced to as low as 1-10% during a span of 48 hours. The precise reasons for larval mortality in sea scallops remain unclear. Prior studies have investigated infections in sea scallops. However, there still needs to be a more extensive investigation into the bacterial communities linked to wild and hatchery-reared deep-sea scallops and the biofilms present in hatchery tanks.

We looked at how the bacteria in tank biofilms in scallop hatcheries might affect the health of the larvae. Downeast Institute, Mook Sea Farm, and Darling Marine Center provided biofilm samples for tests in genomics and microbiology. Every 48 hours, larvae are fine-filtered from all tanks, drained and cleaned, and larvae are put into a fresh tank of filtered seawater. Three biofilm swabs were taken from the bottom of the tank before cleaning and refilling after draining. The study started with samples from adult tanks. Swabs of the tank biofilms were used to grow certain bacteria on thiosulfate-citrate-bile salts-sucrose (TCBS) agar to check for pathogenic Vibrio spp. Plates were transferred to UMaine for gram and endospore staining, testing the bacteria's capacity to utilize sugar and the resistance of isolates to other antibiotics.

The prevalence of yellow isolates (54%) over green isolates (47%) in static tanks suggests the potential presence of different Vibrio species. While flow-through tanks hosted more similar isolate types, at 47% yellow and 50% green isolates. Clean tanks had more sucrose fermenting (51%) than non-sucrose fermenting (41%) isolates. Dirty static and flow-through tanks had higher number of colony growth and a higher prevalence of yellow isolates. Specifically, there were 55% yellow isolates and 30% green isolates in static and dirty tanks, whereas there were 47% yellow isolates and 47% green isolates in flow-through and dirty tanks. Hatchery and scallop farms do not currently use antibiotics in their production, but antibiotic residue from towns and human wastewater can persist in seawater and affect microbes in tanks. We subjected the isolates to antibiotics such as ampicillin, streptomycin, penicillin, and oxytetracycline as a preventive measure against bacterial infections. Streptomycin outperformed all other antibiotics against isolates from various tanks.

Additional Files
Final Thesis_ Ayodeji Olaniyi.pdf (5930 kB)
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