Date of Award

8-2008

Level of Access

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Marine Biology

Advisor

Paul D. Rawson

Second Committee Member

William Halteman

Third Committee Member

Sara M. Lindsay

Abstract

Many commercially important benthic marine invertebrate species have a biphasic life history in which adults release gametes or larvae that develop in the water column until metamorphosis and settlement into adult habitat occurs. These species have high dispersal potential due to passive transport of larvae in prevailing currents. When larvae disperse away from natal areas and successfully recruit, migration among subpopulations increases and little population structure occurs across large spatial scales. This dissertation used multiple approaches to assess the scale of population structure for the sea scallop, Placopecten magellanicus, in the Gulf of Maine. A population genetic analysis assessed variation among sea scallops from Cobscook and Gouldsboro Bays in the eastern Gulf of Maine, Penobscot and Casco Bays in the western Gulf of Maine, and an offshore site on Georges Bank. The results showed that western Gulf of Maine subpopulations, including Georges Bank, were highly differentiated from eastern Gulf of Maine subpopulations, and that the two eastern Gulf of Maine subpopulations were as different from each other as they were from the western Gulf of Maine subpopulations. Further, a genetic analysis of age classes of P. magellanicus from Cobscook Bay revealed significant differences among cohorts. To place the population genetics results in an ecological context, sea scallop settlement in Cobscook Bay was investigated. Both spatial and temporal variation in sea scallop settlement rate was observed. Finally, genetic analyses detect variation in migration that has persisted over many generations, but cannot resolve variation over shorter timescales. The potential for stable isotopes in the larval shell of P. magellanicus to record environmental conditions and identify the origin of recruits was examined. These methods will eventually help estimate short term variation in migration among Gulf of Maine subpopulations. Together, these studies demonstrated that genetic differentiation among sea scallop subpopulations can occur on smaller spatial scales than would be expected based on the life history of the species (10's to 100's km) and that episodic recruitment from more than one source population occurs in Cobscook Bay.

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