Alison Sirois

Date of Award


Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)


Marine Biology


Laurie Connell

Second Committee Member

David W. Townsend

Third Committee Member

Brian Perkins


Maine has more than 3,478 miles of tidal shoreline and commercially valuable shellfish resources in its tidal, sub-tidal, nearshore and offshore waters. From April to October this resource is frequently closed to commercial shellfish harvest for weeks at a time, due to Alexandrium fundyense blooms, the phytoplankton responsible for paralytic shellfish poisoning. The Department of Marine Resources Biotoxin Program (DMRBP) manages the shellfish resource in the nearshore and offshore waters, operating under federal guidelines of the National Shellfish Sanitation Program. Regular weekly shellfish samples are collected at locations throughout the coast to test for elevated toxin levels before, during and after an A. fundyense bloom event, however, because there is no way to predict when and for how long a toxic event will occur, DMRBP begins monitoring weeks in advance of the bloom season and long after toxicity is absent in shellfish. Prior to this study, no effort has been made to determine to what degree cell density can be used as a management tool in Maine. The DMRBP cell enumeration and shellfish toxicity data from Cobscook Bay were analyzed to select a subset of stations most sensitive to toxic events. Of those selected, two stations were chosen and two cell enumeration methods used for cell density during the 2011 bloom: Sedgwick Rafter counting chamber, and fluorescent in-situ hybridization. Daily shellfish samples, Mytilus edulis and Mya arenaria were also sampled at the same locations. Results from this work established cell threshold values for each method for the purpose of predicting the onset of shellfish toxicity in Cobscook Bay. Threshold values are presented as a management tool for inclusion in a tiered sampling approach for monitoring Alexandrium fundyense bloom events. Future work proposes to assess threshold values in other shellfish resource areas along the Maine coast.