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http://www.glerl.noaa.gov/news/seminars/ Date: Wednesday, October 15, 2003 Time: 10:30 a.m. Title: "HISTORICAL RESPONSE OF ZOOPLANKTON COMMUNITIES TO ECOLOGICAL CHANGE IN LAKE VICTORIA (EAST AFRICA)" Speaker: Dr. Thomas Bridgeman Research Assistant Professor University of Toledo, Lake Erie Center Where: GLERL Main Conference Room 2205 Commonwealth Blvd. Ann Arbor, MI 48105 For directions: http://www.glerl.noaa.gov/facil/triptik.html Abstract The introduction of a large predator, the Nile perch (Lates niloticus), caused devastating losses in the fish community of Lake Victoria between 1960-1990, with an accompanying loss of zooplankton and phytoplankton species diversity. Climate change and anthropogenic influences have also been implicated in these losses, but analysis has been confounded by a scarcity of historical records, creating difficulties in determining the timing of changes in zooplankton, phytoplankton, and fish communities in relation to each other. In this study, fossil remains of diatoms, zooplankton (Bosmina, chydorids), and an invertebrate predator (Chaoborus) in sediment cores were analyzed to assemble a 50-year record of changes in the plankton community. The most dramatic changes occurred in the 1980s when several cladoceran species were extirpated from nearshore zooplankton assemblages. These losses corresponded to a rapid shift in the diatom community from dominance by Aulacoseira sp. to Nitszchia sp., and to increasing populations of Chaoborus and the cyprinid planktivore Rastrineobola argentea in nearshore areas. The results suggest that the demise of cladoceran zooplankton resulted from increasing predator densities combined with environmental changes that led to increased hypoxia of bottom waters. An additional example of the importance of stratification and hypoxia in structuring invertebrate communities is given from current research on western Lake Erie mayfly (Hexagenia sp.) recruitment. For more information, contact: Dr. David Reid 734-764-2019 david.reid@noaa.gov -- David F. Reid, Ph.D. U.S. Department of Commerce National Oceanic and Atmospheric Administration Great Lakes Environmental Research Laboratory 2205 Commonwealth Blvd. Ann Arbor, MI 48105-2945 Voice: 734-741-2019 FAX: 743-741-2055 GLERL home page: http://www.glerl.noaa.gov -- David F. Reid, Ph.D. U.S. Department of Commerce National Oceanic and Atmospheric Administration Great Lakes Environmental Research Laboratory 2205 Commonwealth Blvd. Ann Arbor, MI 48105-2945 Voice: 734-741-2019 FAX: 743-741-2055 GLERL home page: http://www.glerl.noaa.gov |