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SEASONAL DOMINANCE OF CYANOBACTERIA IN PENSACOLA BAY, FLORIDA
Citation:
Murrell, M C. AND F J. Genthner. SEASONAL DOMINANCE OF CYANOBACTERIA IN PENSACOLA BAY, FLORIDA. Presented at Fall 2000 Meeting of the Gulf Estuarine Research Society, Hammond, LA, 13-15 November 2000.
Description:
A study was conducted during 1999-2000 in Pensacola Bay, Florida, USA to characterize the seasonal dynamics of nutrients, phytoplankton, and bacterioplankton. Monthly samples were collected from 5 sites spanning the salinity gradient. Abundances of non-heterocystous chroococcoid cyanobacteria (cf. Synechococcus, Synechocystis) became very high (3 X 106 ml-1) during the summer months. Based on concomitant chlorophyll a analysis and microscopic cell counts, we estimated that cyanobacteria contain 1.75 fg chlorophyll a cell-1. Using this calibration we estimated that cyanobacteria accounted for up to 5.25 ?g1-1 chlorophyll in the upper estuary and accounted for ca. 50% of the total chlorophyll (range 11-74%). Similarly, size fractionated bulk chlorophyll analysis showed that the <5 ?m phytoplankton often dominated the community (70-90%).
Flow cytometric analysis of Bay samples from July through October 2000 revealed two distinct communities of cyanobacteria based on their fluorescence characteristics. One type was characterized by strong orange fluorescence under blue excitation (488 nm) suggesting cells rich in phycoerythrin (PE). The other type exhibited deep red fluorescence when excited with a red excitation (610 nm) suggesting cells rich in phycocyanin (PC). The distributional patterns clearly show that PC-rich cells dominated in the upper estuary, while the PE rich cells were more abundant in the lower estuary. In the near-freshwater tidal reach of the Escambia River, abundances were typically one or two orders of magnitude lower than in the nearby estuary suggesting that these are marine cyanobacteria. Ongoing studies are directed at better understanding the factors controlling their abundance and distributional patterns, including the potential role of nutrient limitation.