BENTHIC FORAMINIFERA AND ORGANIC MATTER IN SOUTH SAN FRANCISCO BAY, CA, U.S.A

There are many open questions about the feeding ecology of modern foraminifera and their roles in the cycling of organic carbon in the ocean. My goals are (1) to understand how seasonal changes in sedimentary food resources affect the species composition and population abundances in benthic foraminiferal communities, and (2) to estimate the importance of benthic foraminifera in the cycling of carbon and nutrients in San Francisco Bay, CA, USA. I am monitoring populations of benthic foraminifera and sedimentary food resources monthly at four sites San Francisco Bay from November, 1999 to November, 2001. Four replicate cores are taken at each site for identification and enumeration of live (i.e. stained) benthic foraminifera. Results presented here are for USGS station 25 in South San Francisco Bay. Sediment samples were also taken for measurements of total organic carbon (TOC), chlorophyll a concentration, bacterial abundance, and protein concentration. Foraminiferal population abundances appear to be positively correlated with sediment bacterial abundance in like with the results of previous studies that suggest that bacteria are an important food source for benthic foraminifera. Foraminiferal population abundances also appear to be positively correlated with sediment chlorophyll a concentrations. Given the depth at station 25 (8.8 m) sediment chlorophyll a is most likely a tracer of sedimented planktonic production rather than in situ benthic production. The higher abundances of foraminifera in San Francisco Bay during spring suggest that they are important remineralizers of planktonic production at the sediment-water interface in San Francisco Bay.