HR: 1340h
AN: PP33B-0951    [Abstracts]
TI: The San Francisco Bay Biota Since the Last Sea Level Maximum: Comparing Fossil and Recent Assemblages of Benthic Foraminifera
AU: * Lesen, A E
EM: alesen@pratt.edu
AF: Pratt Institute, Dept.of Math and Science 200 Willoughby Ave., Brooklyn, NY 11205 United States
AU: Lipps, J H
EM: jlipps@uclink.berkeley.edu
AF: Unversity of California, Berkeley, Dept.of Integrative Biology 3060 Valley Life Science Building, Berkeley, CA 94720-3140 United States
AB: Comparisons of fossil and Recent foraminiferal assemblages in San Francisco Bay can give us information about how the Bay's ecosystems have changed or remained resilient during the glacial cycles of the Pleistocene. This information, in turn, can help us to predict the potential impact of future environmental change on this system. In this study, we compared the species proportions, overall similarity, and species diversity of the Recent foraminiferal assemblage at one site in South San Francisco Bay with the fossil foraminiferal assemblage from Pleistocene samples taken at several sites in South San Francisco Bay, in order to test the hypothesis that the foraminiferal assemblage in San Francisco Bay has not changed significantly since the last interglacial interval. Comparisons of total sample similarity indicate that the upper layer of the Yerba Buena mud was deposited during conditions similar to today's South San Francisco Bay. The presence of a large number of dead tests of Elphidium gunteri Cole and Elphidiella hannai (Cushman and Grant), together with the lack of living populations of these species in South San Francsico Bay, make it difficult to interpret the presence of these taxa in similar abundances in the Plestocene and today. Possibly due to the introduction of the Japanese foraminifer Trochammina hadai Uchio, the modern assemblage has shifted away from the dominance of Elphidium excavatum (Terquem) found in the Pleistocene. Species diversity has neither decreased nor increased between the Pleistocene and the present day in South San Francisco Bay, suggesting that environmental change and human activity has not affected species diversity of the benthic foraminiferal fauna. These data show that comparisons between fossil and Recent assemblages are powerful tools in interpreting paleoenvironments, and may help us to understand the impact of human activity on estuarine and other marine systems. More research is needed on the living populations of E. gunteri and E. hannai today to be able to interpret the significance of these populations in the Pleistocene bay.
DE: 4840 Microbiology
DE: 4235 Estuarine processes
DE: 4267 Paleoceanography
DE: 4804 Benthic processes/benthos
DE: 3030 Micropaleontology
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting