Algal Blooms and Plankton Ecology

Florida Bay Microalage

Florida Bay Project Profile - 39

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Questions: Which microalgae are responsible for the blooms in the different regions of the bay? What regions experience the most intense blooms?

Background/Project: Microalgal blooms have persisted in some areas of Florida Bay since the early 1990’s. These dense populations of microscopic algae (often called phytoplankton to describe their drifting lifestyle) may be detrimental to Florida Bay because they discolor the water causing reduced clarity. Changes in the microalgal populations may also affect the kinds of animals and plants supported by the bay’s food web.

From May 1994 through May 1997, BayWatch volunteers from The Nature Conservancy and Florida Marine Research Institute scientists collected monthly water samples from six permanent and many other sites in the bay. At the time of sampling, water temperature, salinity, and water clarity were recorded. Using a compound microscope, the microalgae were identified and counted. Water samples collected in the field were analyzed for their chlorophyll-a content.

Findings to Date: Different regions of the bay had different resident populations of microalgae. The persisitent blooms of the north central bay were often dominated by a cyanobacterial (primitive blue-green) species. Depending upon the seasonal conditions, northern blooms also consisted of species of yellow-brown diatoms and various flagellates including large dinoflagellates. The "brown" turbid blooms in the western bay were a mixture of yellow-brown diatoms and high amounts of resuspended bottom sediments including organic material which may serve as a nutrient source for the microalgae. The western bay had the highest suspended sediments in the water column. Chlorophyll-a values allowed scientists to compare the intensity of the blooms in the different areas. Values were highest in the north and central regions (from .29 to 40 micrograms per liter, µg/L), followed by the western region, which at times had values over 20 µg/L. Generally, values over 20 µg/L are indicative of nuisance blooms. Storms and high winds influence the spread of bloom water—sometimes driving blooms from the north toward the south and the west and at other times driving western water toward the central bay.

Status: Sampling was completed in 1997; analyses are in progress.

Funding Source: Florida Marine Research Institute

Restoration Impacts: Information about microalgal bloom species enables managers to better predict the outcome of changes in Everglades surface water flow on bay water quality.

Related Profiles: • FBPP 32 • FBPP 36 • FBPP 58