What is the abundance and distribution of zooplankton (animals which drift in the water column) in Florida Bay? How
do the grazing rates of zooplankton on phytoplankton
compare with the production of new phytoplankton
Background/Project: Historically, seagrasses (and their epiphytes) grazed upon by fish and invertebrates were considered to be the most important plants in Florida Bay. With recent widespread losses in seagrasses and persistent phytoplankton blooms, the role of zooplankton both as consumers of phytoplankton and/or bits of decayed plant material (detritus) and as food for juvenile fish may be more important than in the past. Using plankton tow nets and water bottles, samples of larval fish, crustaceans, snails, and other zooplankton are collected on a bimonthly basis from eight permanent sites representing different regions in the bay. Key zooplankton species are being identified using microscopic techniques. Grazing rates of the most abundant zooplankton, the copepods, are estimated for each copepod taxonomic group using the estimated ingestion rate for that copepod and its abundance. Grazing rates by other zooplankton are also being calculated in a similar way.
Findings to Date: Zooplankton are moderately abundant throughout the year. In some seasons, molluscan larvae are the most abundant, but otherwise copepods, including Acartia tonsa, dominate. In general, zooplank-ton are most abundant in the western bay where blooms of phytoplankton occur frequently and least abundant in the eastern bay where blooms rarely occur. Being consumed by zooplankton is the primary cause of mortality in phytoplankton. In bloom areas, the grazing rates of zooplankton did not keep up with the production of new phytoplankton material. In contrast, in the eastern bay where phytoplankton populations are low, grazing rates were equal to production rates.
Status: The study originated in 1994 and will continue through 2000.
Restoration Impacts: The data collected about phytoplankton and zooplankton is essential to modelers concerned with water quality and energy flows through the Florida Bay food web. This information may help scientists to better predict population trends in predatory gamefish species.
Funding Sources: National Oceanic Atmospheric Administration , National Ocean Service Coastal Ocean Program; Florida Marine Research Institute (past)