Date of Award

Spring 5-2018

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Marine Biology

Advisor

Lawrence Mayer

Second Committee Member

Paul Rawson

Third Committee Member

Damian Brady

Additional Committee Members

Carter Newell

Abstract

Oyster aquaculture is an expanding industry that relies on identifying and utilizing natural estuarine conditions for the economically viable production of a filter-feeding crop. The eastern oyster, Crassostrea virginica, is the principal species currently cultured in Maine. In addition to preferentially consumed phytoplankton, various detrital complexes (non-algal and/or non-living organic matter) may provide some nutrition to C. virginica between times of phytoplankton abundance. Here I investigated the importance of detrital proteins in supporting the growth of oysters cultured in the upper Damariscotta Estuary. Oyster aquaculture in this area is highly successful and previous reports indicate that labile detrital protein is seasonally abundant.

I coupled in vitro chemical assays of seston quantity and quality (protein lability is a key parameter of quality) with in vivo bioassays of feeding and growth of C. virginica to test the hypothesis that detrital protein contributes to oyster nutrition in the Damariscotta Estuary. From May to October 2016, enzymatically hydrolyzable amino acids (EHAA, labile protein), extracted chlorophyll-α (CHL), particulate organic matter (POM), and plankton abundance (via FlowCam) analyses were conducted biweekly along with continuous monitoring of temperature, turbidity, and CHL by a Land/Ocean Biogeochemical Observatory (LOBO) buoy. Oyster feeding and growth were measured biweekly under natural conditions and in a controlled laboratory experiment to assess responses to detrital food.

Oysters readily absorbed phytodetritus (dead and decaying phytoplankton) under laboratory conditions and cleared phytodetritus under natural field conditions. Additionally, estimates of POM absorption rates indicate that oysters absorbed more organic matter than was available from phytoplankton alone, suggesting a role for additional organics such as detritus in oyster nutrition. Bioavailable EHAA was nearly completely absorbed by oysters, consistent with EHAA limitation of dietary demand. Seasonal EHAA concentrations correlate well with growth rates (along with temperature, turbidity, and ciliate abundance), corroborating protein limitation of oyster growth. Finally, not all EHAA can be attributed to phytoplankton throughout the season, implying seasonally abundant labile detrital protein. Considering the strong influence of EHAA abundance on this aspect of biota in the Damariscotta Estuary, EHAA measurements may prove helpful in future studies of both aquaculture site selection and ecological nutrient flows.

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