SPATIAL VARIABILITY IN PHYTOPLANKTON STANDING CROP AND COMPOSITION INA SHALLOW INNER-SHELF LAGOON, FLORIDA-BAY, FLORIDA

Spatial and temporal patterns of phytoplankton standing crop and compo sition in Florida Bay were studied for a 6-month period. Significant s patial differences were observed supporting the hypothesis that the ba y is composed of a number of ecologically distinct regions. The highes t standing crops of planktonic algae and cyanobacteria were found in t he central-interior region of the bay, where the small unicellular cya nobacterium Synechococcus dominated the planktonic assemblage. Chlorop hyll a concentrations ranged from 8-40 mg m(-3) in this region, and Sy nechococcus was responsible for nearly 100% of total phytoplankton bio volume. In other regions of the bay total chlorophyll a concentrations were significantly lower and the relative importance of diatoms and d inoflagellates increased in relationship to total phytoplankton biovol ume. Model relationships between chlorophyll a and total nutrient conc entrations supported the commonly held view that the primary limiting nutrient in the bay may be phosphorus. However, the strong presence of a potentially nitrogen-fixing species of cyanobacteria indicates that nitrogen must be considered in evaluating the limiting status of plan ktonic primary production.