Date of Award

Spring 5-8-2020

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Marine Biology

Advisor

Carrie J. Byron

Second Committee Member

Damian C. Brady

Third Committee Member

Barry Costa-Pierce

Additional Committee Members

Lawrence M. Mayer

Christopher C. Parrish

Abstract

Detritus is a ubiquitous component of ecosystems and an important fuel for secondary production. Due to the extractive nature of bivalve aquaculture, detritus is often incorporated into carrying capacity and growth models for cultured bivalves. However, despite the complexity and difficulty in obtaining direct measurements, detritus is often treated as a homogeneous food source in models. Further understanding the role detritus plays in the diet of cultured bivalves could lead to more comprehensive and accurate models as well as more informed site selection for growers. The purpose of this study was to assess the abundance, bioavailability, and contribution of detritus to the diet of a commercially important bivalve (Mytilus edulis) in a northern temperate bay (Saco Bay, ME USA) using a combination of lipid fatty acid biomarkers and stable isotopes (δ13C and δ15N). Both macroalgal (6.9 ± 0.1%) and vascular plant (4.8 ± 0.1%) detritus contributed to the particulate organic matter of Saco Bay and could supplement essential fatty acids (FA) or their precursors to consumers able to digest them. Mussels in Saco Bay may have been limited by the availability of the essential fatty acid 20:5ω3 (EPA) and incorporated macroalgal detritus as a small part (5 to 11%) of their diet. Macroalgae contained large proportions of the essential FAs 20:4ω6 (7 to 18%) and 20:5ω3 (8 to 25%) which may supplement the dietary needs of mussels. The original source of primary production had more influence on the bioavailability of lipid and FAs than the state of decay. The bioavailability of lipid and FAs from Ascophyllum nodosum (9 ± 3%) was significantly lower than that of Spartina alterniflora (56 ± 19%) and Isochrysis galbana (48 ± 2%), likely due to the presence of polyphenols and structural alginates that interfered with lipid solubilization. Although it contains essential FAs and its contribution into the diet of M. edulis suggest macroalgae could be a good supplemental diet for bivalve aquaculture, the concentration of secondary metabolites (>3% wt/wt) and alginates needs to be considered due to their anti-nutritional effects.

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