Date of Award

12-2003

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Marine Biology

Advisor

Paul D. Rawson

Second Committee Member

Bruce Barber

Third Committee Member

J. Malcolm Shick

Abstract

Two species of blue mussel, Myrilus edulis and Myrilus trossulus, are sympatric throughout much of the Canadian Maritime Provinces and into the Gulf of Maine. While the distribution of M edulis extends south to the Mid-Atlantic, that of M. trossulus ends abruptly in the Gulf of Maine. I have hypothesized that these differences in adult distribution are the result of species-specific variation in larval thermal tolerances. Previously, it has been shown that when reared at 20 OC, from 36 hour post-fertilization through settlement, M. trossulus had significantly higher mortality rates than M. edulis. This study examined whether species-specific differences in thermal tolerance vary during larval development. Larvae of both species were exposed to three experimental temperatures at three time points during development and growth and mortality were monitored. Larval thermal tolerance for both species changed significantly as a function of age. Instantaneous mortality was highest during the first ten days of development and decreased to the lowest rate during the second ten days of development. Unexpectedly, there were no significant differences in mortality between M. edulis and M. trossulus larvae in any of the age-temperature treatments used in this experiment. These results stand in contrast to those from previous experiments and raise doubt as to whether the steep thermal gradient created by the Eastern Maine Coastal Current limits the distribution of M. trossulus.

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