SPECTRAL REFLECTANCE-BASED OBSERVATION OF DIATOMS AND DINOFLAGELLATES IN HARPSWELL SOUND, MAINE

Annual spring blooms of the phytoplankton Alexandrium fundyense in the Gulf of Maine are problematic for human health and the Maine economy.  Neurotoxins produced by A. fundyense accumulate in shellfish, leading to the potential for Paralytic Shellfish Poisoning (PSP) in humans who consume the shellfish.  One proposed method for the observation of A. fundyense is the use of satellite remote sensing.  However, A. fundyense is difficult to monitor directly since it is usually not a major component of the total phytoplankton population.  To account for this, the presence of dinoflagellates is used as a proxy for A. fundyense, since microscopic cell count data has shown a correlation between the presence of dinoflagellates and A. fundyense.  Water samples were collected in Harpswell Sound two times per week from March to August 2008, and once per week in September and October 2008.   Microscopic cell counts were used to determine dates when dinoflagellates or diatoms were present as the majority of the phytoplankton population.  HPLC pigment analysis from the same dates and times shows that the presence of differently absorbing carotenoid pigments is well correlated with the two phytoplankton groups.  Measured absorption values were then analyzed, and differences in absorption spectra were observed on days when dinoflagellates or diatoms made up the majority of the phytoplankton population.  Finally, dates with known differences in absorption will be used to look for differences in spectral reflectance, which was measured with a Satlantic TSRB buoy deployed in Harpswell Sound from May 14 to October 10 2008.  It is expected that differences in absorption will indicate differences in spectral reflectance, since reflectance varies inversely with changes in absorption spectra.  Modeled spectral reflectance of different absorption components show that the presence of the two phytoplankton groups can be discerned based on measured reflectance.  After the reflectance model has been validated, an inverse reflectance model will be applied to reflectance data from May through October 2008.  This data, combined with other hydrological data, will allow some insight into the dynamics of A. fundyense in Harpswell Sound and the abilities of satellite remote sensing to detect its presence.