Algal Blooms and Plankton Ecology

Algal Bloom Maps of Florida Bay

Florida Bay Project Profile - 44 (SGEF- 98)

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Question: What were the trends in size and distribution of microalgal blooms in Florida Bay from 1994 to 1997?

Project/Background: This project entailed mapping the distribution of microalgal (phytoplankton) blooms and turbid waters over a 3,000 square mile region of Florida Bay and the Florida Keys. Although this method is subjective, it has shown to be an effective (rapid, coast efficient, repeatable) means to obtain comparative snapshots of the distribution of blooms and turbidity.

The analysis of water samples collected from the bay by The Nature Conservancy Bay-Watch Volunteers and FMRI scientists at the time of the aerial survey showed that the turbid and bloom water fell into five major water categories. These were: murky due to suspended sediments; murky due to high microalgal concentrations; murky due to a mixture of the two factors; brown in color because of a natural association with nearby wetlands; and clear or free of turbidity. A map showing the distribution of bloom and turbid water by category was constructed based on the results of each fly-over survey.

Findings: Two major types of blooms are found in Florida Bay. The decay of seagrass plants which began dying in the late 1980's are thought to have provided nutrients that fuel the blooms. The north central bay bloom is caused by high concentrations of a primitive blue-green algae mixed with a variety of other microalgae. The western bay bloom is referred to as a mixed bloom because it contains various species of microalgae mixed with suspended limestone sediments and bottom-dwelling (benthic) microalgae stirred up from the bay bottom. To assess overall trends in bloomsize and distribution, an annualized map for each year was produced. These maps showed how many months of the year bloom conditions occurred in the different parts of the bay. In 1994, some areas in the north central bay experienced bloom conditions more than nine months of the year, while blooms were not observed at all in the eastern bay. The persistent bloom of the north central bay covered 104 square miles in 1994, but covered only 18 square miles in 1996. A similar significant decrease in bloom coverage in 1996 was also noted for the mixed bloom in the western bay.

Several environmental and biological factors may have contributed to the declines in blooms noted in the bay. The ending of regional drought conditions in 1994 brought salinity levels down in bay surface waters. These more moderate conditions may provide favorable habitat for microalgal species other than those which dominated the blooms. In addition, the nutrient supply, decaying seagrasses, may be dwindling since seagrass mortality has slowed in some areas and presumably much of the original decaying plant material has already been used up by microalgae.

Status: All maps generated by this project have been incorporated into an ARC/INFO GIS (geographic information system) for further analysis of the seasonal patterns and movement patterns of bloom waters.

Restoration Impacts: The maps of microalgal blooms in Florida Bay and associated water quality analyses have provided ecosystem managers and scientists with a better understanding of bloom dynamics and patterns.

Funding Sources: The Nature Conservancy, Florida Marine Research Institute

Related Profiles: • FBPP 34 • FBPP 36 •FBPP 39