Phytoplankton Dynamics in Harpswell Sound, Gulf of Maine

Advisor Name

Collin S. Roesler

Advisor Affiliation

Bowdoin College

Document Type

Conference Proceeding

Publication Date



In the Gulf of Maine, Harpswell Sound is a sentinel area for signaling the onset of harmful algal blooms (HAB). During HAB events the coastal shellfish industry in the Gulf of Maine must be closed. For the past three years the factors responsible for dramatic increases in the abundance of the harmful dinoflagellate Alexandrium fundyense have been studied using a combination of discrete sampling and time series from an hourly reporting oceanographic buoy. Phytoplankton samples have been taken and counted during this period. Variation in the timing and intensity of the blooms species A. fundyense has been sporadic. In 2008 two large blooms of dinoflagellates (cell abundance greater than 25,000) occurred between May and August and only one large dinoflagellate bloom in 2009. Nutrient data was taken during the time of plankton sampling for both years. Since limited samples were taken in both years at arbitrary timing of the tides, correlating nutrient data with phytoplankton concentrations is difficult. In 2008 peak concentrations of phosphorus either immediately preceded or coincided with large blooms of dinoflagellates. This relationship between phosphorus and dinoflagellates was not observed in 2009. This suggests that factors controlling the phytoplankton ecosystem in these two years varied. Further exploration of offshore impacts on costal chlorophyll and phytoplankton concentrations will give more insight into the cause and timing of these blooms. Chlorophyll concentrations from six buoys from the Gulf of Maine Ocean Observation System will be analyzed to determine if there is evidence for export of HABs from the Gulf of Maine into Harpswell Sound. Correlation to the oceanographic buoy in Haprswell Sound will give more insight into the connection between offshore chlorophyll concentrations and near shore dynamics.


Samuel J. Hankinson and Gregory J. Teegarden were undergraduate students at Bowdoin College and St. Joseph's College when this research was conducted.