Date of Award

Spring 5-20-2025

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Marine Biology

First Committee Advisor

Damian Brady

Second Committee Member

Romain Lavaud

Third Committee Member

Emmanuel Boss

Additional Committee Members

Gary Wikfors

Paul Rawson

Abstract

Marine shellfish aquaculture faces significant challenges in understanding animal growth because of the complex and dynamic nature of nearshore ocean environments. This dissertation employs statistical and mechanistic modeling techniques to examine and predict the growth of cultured eastern oysters and sea scallops in Maine, addressing key gaps in aquaculture development for the Northwest Atlantic region.

The first chapter of this work focuses on the Atlantic sea scallop (Placopecten magellanicus), a species prized in U.S. seafood markets yet underdeveloped in aquaculture. We evaluated the effects of culture method, husbandry, and environment on scallop shell growth and mortality, compiling 45 years of data from the Northwest Atlantic. Using generalized additive models (GAMs), we identified significant nonlinear interactions between environmental conditions and husbandry. Optimal shell growth occurred at temperatures between 10 – 15 °C, was higher in pearl nets compared to lantern nets, and decreased with increased stocking density. Mortality peaked at temperatures above 17 °C and was more pronounced at high stocking densities and for scallops with shell heights under 25 mm. These findings emphasize the importance of temperature-based site selection and low-density stocking to enhance scallop growth and reduce mortality, providing actionable guidance for expanding scallop aquaculture in the Northwest Atlantic.

The second chapter examines the culture performance and physiology of triploid eastern oysters (Crassostrea virginica) in Maine. Triploid oysters have become a crucial tool for aquaculture because of their rapid growth rates and reduced reproductive activity compared to diploids. While extensively adopted in regions along the U.S. East Coast, limited research has evaluated triploid oyster performance in the colder waters of the Northwest Atlantic where the growing season is shorter. Over a 17-month study at two farm sites, triploids exhibited 22% greater shell height and 53% greater tissue mass than diploids. Triploid growth was higher when water temperatures were above 17°C and when food concentrations were greater than average. Despite their rapid growth, triploids and diploids displayed similar oxygen consumption rates during a 10-week starvation experiment, although diploids lost tissue mass more rapidly. These results demonstrate the growth advantages of triploid oysters in northern environments and highlight the need to match ploidy with local environmental conditions for optimal production efficiency.

The last chapter addresses the broader challenge of site selection for shellfish aquaculture by using high-resolution remote sensing data to model growth and predict time-to-market for eastern oysters in Maine’s nearshore environments. We developed a dynamic energy budget model for the Northeast U.S. eastern oysters and validated it with extensive growth data. High-resolution satellite data, including sea surface temperature from Landsat 8 & 9 as well as chlorophyll-a and POM estimates from Sentinel 2, proved effective in identifying optimal growing regions. This approach provides a powerful tool for aquaculture site selection and supports the expansion of marine aquaculture in complex nearshore coastal ecosystems.

By using both statistical and mechanistic modeling techniques, this dissertation offers critical insights into optimizing shellfish aquaculture in the Northwest Atlantic. The findings provide practical guidance for site selection, cultivation strategies, and understanding the interplay between environmental conditions and shellfish growth, advancing the sustainable development of marine aquaculture.

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