Benthic foraminifera in San Francisco Bay: Environment, ecology and paleoecology

The seasonal nature of the San Francisco Bay ecosystem, the long history of ecological research, and availability of long-term data in San Francisco Bay make it an ideal system in which to explore outstanding questions about organic matter cycling and trophic dynamics in estuaries. Benthic foraminifera are abundant, have a long fossil record, and are a link between low and high trophic levels and are important in the cycling of organic matter and organic carbon. Using San Francisco Bay as a model system, I investigated patterns of benthic-pelagic coupling, looked at the relationship between benthic foraminiferal population dynamics and sediment organic matter, and compared the paleontological record with present day assemblages of benthic foraminifera.; Quantification of water column chlorophyll-a and sediment parameters on a monthly basis over a two year period from November 1999 through November 2001 at four sites in San Francisco Bay revealed benthic-pelagic coupling in the bay, and seasonality in both water column chlorophyll and sediment organic matter. Investigation of Rose Bengal stained benthic foraminiferal population dynamics at one site in South San Francisco Bay showed that the total numbers of benthic foraminifera increased when sediment organic matter was high. The population was dominated at high levels of organic matter by one taxon, the foraminifer Fursenkoina pontoni suggesting that this species is able to increase its populations rapidly ay high levels of organic carbon. The introduced foraminifer, Trochammina hadai, decreased at high levels of organic matter; this suggests that T. hadai may not be a good competitor when sediment organic matter is high. Comparison of Recent and Pleistocene total foraminiferal relative abundance in South San Francisco Bay indicates that the upper layer of the Yerba Buena mud was deposited during conditions similar to today's South San Francisco Bay. The modern foraminiferal assemblage has shifted away from the dominance of E. excavatum found in the Pleistocene, to dominance by the introduced foraminifer T. hadai. Species diversity has not changed significantly between the Pleistocene and the Recent in South San Francisco Bay, suggesting that environmental change and human activity has not affected species diversity of the benthic foraminiferal fauna.