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GRAZING AND NUTRIENT LIMITATION STUDIES IN PENSACOLA BAY: THE ROLE OF TOP-DOWN VERSUS BOTTOM-UP CONTROLS
Citation:
Murrell, M C., E M. Lores, AND R S. Stanley. GRAZING AND NUTRIENT LIMITATION STUDIES IN PENSACOLA BAY: THE ROLE OF TOP-DOWN VERSUS BOTTOM-UP CONTROLS. Presented at Gulf of Mexico Symposium 2000, Mobile, AL, April 9-12, 2000.
Description:
To better understand the causes and consequences of nutrient over-enrichment (eutrophication) in Gulf of Mexico estuaries, we examined the roles of grazing and nutrient limitation in Pensacola Bay. One consequence of eutrophication is altering the function of plankton food webs; the basis of the marine food chain. Such an alteration can have cascading effects on the entire ecosystem and result in multiple negative impacts including loss of habitat and loss of human resource use. Microzooplankton grazing and nutrient limitation studies were conducted in the Pensacola Bay system at two sites on 5 dates from December 1998 to September 1999. The grazing experiments examined the potential top-down control on primary production, while the nutrient limitation experiments examined bottom-up controls. The grazing experiments measured changes in net phytoplankton growth in treatments with varying numbers of microzooplankton predators. Preliminary results suggest that microzooplankton often exerted a significant mortality (46% to over 100% of production) on phytoplankton communities. The nutrient limitation experiments measured the growth of phytoplankton in treatments with varying nutrient additions. Those results suggest that phosphorus may limit primary production at certain times of the year. Combining these results allows a means to evaluate the relative importance of top-down and bottom-up controls on primary production.