Late Spring and Summer Phytoplankton Community Dynamics on Georges Bank with Emphasis on Diatoms, Alexandrium SPP., and other Dinoflagellates

• Main Author: Gettings, Rachel
• Format: Text
• Language: unknown
• Published: DigitalCommons@UMaine 2010
• Subjects: Dinoflagellates Georges Bank; Phytoplankton Georges Bank; Oceanography; Oceanography and Atmospheric Sciences and Meteorology; Northwest Atlantic
• Online Access: https://digitalcommons.library.umaine.edu/etd/122; https://digitalcommons.library.umaine.edu/context/etd/article/1126/viewcontent/GettingsR2010.pdf

Georges Bank is a highly productive continental shelf system in the Northwest Atlantic that has historically supported a rich fishery. Part of that productivity stems from annual spring diatom bloom, which is followed by post-bloom populations of flagellates, including the toxic dinoflagellate Alexandrium spp., responsible for paralytic shellfish poisoning. While the general oceanography of Georges Bank has been well studied, far less is known about phytoplankton community dynamics or even basic species distributions and abundance. This thesis is driven in part by the possible competitive interactions among species of phytoplankton which are thought to influence Alexandrium blooms on the Bank. I examined the distribution, abundance, and succession patterns of the major species groups of diatoms, dinoflagellates, and nanoplankton on Georges Bank from late spring through summer 2008 (late April, May and June). Those results were related to dissolved inorganic nutrients, total and size-fractioned chlorophyll concentrations, and hydrography (temperature and salinity). The late April phytoplankton community was predominantly diatoms, mainly Skeletonema spp., Thalassiosira spp., Coscinodiscus spp., and Chaetoceros spp. with cell densities of > 200,000 cells L"1; reduced nutrient concentrations over most of the Bank, except the northern portions, indicated that this marked the end of the spring bloom. Lower nitrate (and silicate) concentrations in May, and patches of slightly elevated ammonium, were supporting a dinoflagellate population with high cell densities of Alexandrium spp. (up to 13,000 cells L"1). Diatom cell densities were fewer than 40,000 cells L"1 and did not overlap spatially with the high cell densities of Alexandrium spp. Localized patches of elevated silicate (from regeneration) observed in late May cruise appeared to support a post-bloom, summer diatom community (> 180,000 cells L"1), of species of Leptocylindrus spp., Dactyliosolen spp., and Guinardia flaccida. Continued reduction of nutrient ...