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LONG-TERM PLANKTON MONITORING OF LAKE OKEEECHOBEE, FLORIDA: TRENDS IN CRUSTACEAN ZOOPLANKTON POPULATIONS AND COMPARISON TO OTHER SHALLOW SUBTROPICAL LAKES

John R. Beaver BSA Environmental Services Beachwood, OH Karl E. Havens University of Florida Gainesville, FL Therese L. East South Florida Water Management District West Palm Beach, FL

Long-term plankton monitoring of the plankton of Lake Okeechobee was conducted from 1994 to 2006 to examine relationships among zooplankton composition, phytoplankton composition, and potential controlling physical/chemical variables. The crustacean zooplankton assemblage of Lake Okeechobee was typical of other eutrophic Florida systems, being numerically dominated by the calanoid copepod Diaptomus dorsalis, which is considered to be more successful in productive Florida lakes because of both its higher population growth rate and its greater ability to avoid vertebrate predators than other crustaceans. Cyclopoid copepods were much less important, in terms of their relative abundance or biomass. Like other productive Florida lakes, cladocerans were less important than copepods and were dominated primarily by Eubosmina tubicen and to a much lesser extent by Daphnia ambigua. Abundance of both calanoid copepods and cladocerans generally decreased with decreasing water depth, perhaps indicating that deep-water stations provide a vertical refuge from predators that is not available in shallow near-shore locations. Despite several significant perturbations to Lake Okeechobee during the 12-year study (including a drawdown, drought, and four hurricanes), the crustacean zooplankton community remained taxonomically unaltered with similar densities and seasonality throughout the study with the exception of a decline in cladocerans after the drought. The abundance of crustacean zooplankton components was poorly correlated with variables related to food quantity/quality and physical/chemical variables. The similarity of the crustacean zooplankton community of Lake Okeechobee to other shallow lakes in Florida and the temperate zone will be discussed.

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NOTES

Session 3 – Page 4

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