Date of Award

Spring 5-3-2024

Level of Access Assigned by Author

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Oceanography

Advisor

Damian C. Brady

Second Committee Member

Lawrence Mayer

Third Committee Member

Jeremy Testa

Additional Committee Members

Joseph Salisbury

Aaron Strong

Abstract

The Gulf of Maine is a highly productive shelf sea in the Northwest Atlantic Ocean that supports many important commercial shellfish. The Gulf of Maine has naturally low calcium carbonate saturation states (𝛀) due to its relatively cold and fresh waters. 𝛀 has been shown to be important predictors of larval and juvenile shellfish growth and mortality. Many of these shellfish species spend all or part of their life cycle within the estuaries that fringe the Gulf of Maine and shellfish aquaculture within the estuaries is increasing rapidly. The 𝛀 of these estuaries are poorly understood, particularly on high frequency time scales such as days to months. 𝛀 has been shown to be highly variable in estuaries due to the increased rates of physical and biogeochemical processes that impact it and alterations due to human activity.

To better understand 𝛀 variability in two Maine estuaries, I studied the relationship between 𝛀 variability and physical, chemical, and biological processes that impacted 𝛀, and identified why those processes were changing. In the upper Damariscotta River, I found that 𝛀 varied both on a seasonal scale via changes in temperature and salinity, as well as on weekly time scales related to tidal cycles. These shorter timescale variations were correlated with changes in dissolved oxygen concentration, turbidity, and chlorophyll, indicating that ecosystem metabolism was likely the main driver of these changes.

The upper Damariscotta River is also the largest oyster growing area in northern New England. I looked at the impact of oyster growth on 𝛀 using 2018 industry size and oceanographic conditions and found that calcification and respiration rates could lower 𝛀 by 2-3% over the course of the growing season. Increased industry size or continued ocean acidification further decreased 𝛀 in the growing area. This is relevant to the industry because lower 𝛀 could reduce the shell thickness of the oyster and lead to more breakage during processing or increased predation.

Last, I estimated 𝛀 for three sites in Casco Bay, Maine that had different watershed inputs and identified drivers of 𝛀 change and how they differed from site to site. Net ecosystem metabolism was the largest driver of 𝛀 variability at all three sites, however temperature and salinity also played a role in 𝛀 over weekly to monthly scales. Portland Harbor, which had the highest rates of industrialization in the watershed and surrounding waters had the lowest 𝛀, metabolic rates, was net heterotrophic July - October, and had the lowest temperature and salinity.

Overall, daily - monthly variations in 𝛀 were large and dependent on both the physical and biogeochemical processes in these estuaries. Understanding these changes in estuaries is the first step in designing experiments that accurately represent what shellfish are experiencing in situ and will provide more realistic expectations for how shellfish will respond to future changes in 𝛀.

Download

Files over 10MB may be slow to open. For best results, right-click and select "save as..."

Share