Distributions of phytoplankton in Tampa Bay Estuary, USA 2002-2003

Phytoplankton was observed from April 2002 to April 2003 in Tampa Bay to determine spatial and temporal patterns of composition and abundance. Picoplankton cyanobacteria were numerically dominant at all sites within the bay, but due to their small size were infrequently dominant in terms of biomass (i.e., biovolume). The small-celled diatoms Skeletonema and Pseudo-nitzschia were the next most numerically abundant taxa throughout the bay. In terms of biovolume, the dominant species varied spatially and temporally. Diatoms dominated in the lower and midbay, with the relative abundance of large-celled diatoms, such as Dactyliosolen fragilissimus, higher in the lower bay (near the outlet to the Gulf of Mexico) than in the mid-bay region. In the upper bay, dinoflagellates were most often dominant. During the summer and fall, a bloom of the potentially toxic dinoflagellate Pyrodinium bahamense var bahamense was observed in the upper bay, with cell densities up to 350 cells L-1. Our observations are consistent with the hypothesis that different sub-basins of the bay support different phytoplankton assemblages. From a historical perspective, the most dramatic distinctions between past records and our results were the previous absence of Pyrodinium bahamense var. bahamense blooms, and the first report of picoplankton.