Patterns and Scales of Phytoplankton Variability in the Coastal Waters of West Florida Shelf.

Coastal oceans are one of the most dynamic and productive aquatic ecosystems, often characterized by rich phytoplankton assemblages. Increased anthropogenic pressure along with myriad other stressors such as eutrophication, harmful algal blooms, hypoxia and climate change have raised significant concerns on improved understanding the health of these systems. Diversity, abundance and composition of the phytoplankton community are one of the fundamental indicators that determines the productivity and overall health these systems.

As a part of the collaborative programs with FWC/FWRI, Mote Marine Laboratory has been collecting biological and environmental data for nearly two decade. Taxonomic composition, size indices and biomass of phytoplankton community were determined through HPLC analysis of phytoplankton pigments, microscopic cell counts and flowCAM data. The major taxonomic groups included diatoms, dinoflagellates (dominated by Karenia brevis) and cyanobacteria. Patterns and scales were extracted from the phytoplankton abundance, composition data. High phytoplankton biomass (chlorophyll-a) events typically initiate by July and persist through the fall. Blooms of dinoflagellate Karenia brevis followed the high biomass trends and sometimes precede cyanobacterial and sporadic diatom blooms. However, there were no consistent interannual patterns of recurrent spring blooms. To identify the factors controlling the phytoplankton variability on different temporal scales the data-set was subjected to multivariate statistical analysis. Preliminary analysis indicates seasonal and temporal variations phytoplankton abundance and composition were closely related to river discharge along with nutrients particularly silicate and nitrates. Strong correlations between the community structure and environmental variables were found during and between Karenia brevis blooms. Quality controlled phytoplankton time series data sets such as these are critical in understanding biogeochemical cycling and long term changes in the coastal ecosystems worldwide.