Dissertations, Theses, and Capstone Projects

Date of Degree


Document Type


Degree Name



Earth & Environmental Sciences


Brett F. Branco

Committee Members

Juergen Polle

Gregory O'Mullan

Gary H. Wikfors

Subject Categories

Environmental Microbiology and Microbial Ecology | Marine Biology


mercenaria, mortality, n-3 fatty acids, decreasing temperature, homeoviscous adaptation


The series of investigations described in this thesis were designed to assess the effect of diet on mortality through decreasing temperature in two genetic varieties of M. mercenaria important to the natural environment and the aquaculture industry: “wild” from natural stocks and “notata” selected for fast growth. Data from these novel investigations demonstrate a temperature specific sensitivity to each dietary component designating 20:5n-3 as homeoviscously favorable in the upper thermal range above 12°C, and 22:6n-3 as favorable in the lower. Statistical analyses of variance demonstrate distinct cumulative mortalities among the 5 dietary treatments (P < 0.05) for each genetic variety at each thermal range, upper (>12°C) and lower (2 = 0.9326 and 0.6966, respectively, for variable dietary DHA abundances in the lower range (n = 15); and positive relationships with low variance of mortality of wild and notata, R2 = 0.6002 and 0.8622, respectively, for EPA when incorporated as “unfavorable” within the lower thermal range (n = 12). These findings introduce a framework for understanding the relationship between plankton fatty acids and juvenile quahog mortality through seasonally decreasing temperature. They also present a potentially useful measure in the quahog aquaculture industry to reduce mortality through decreasing temperatures: dietary treatments tailored to thermal range. Future research will be necessary to fully realize this potential.