MEPS 297:131-145 (2005)  -  doi:10.3354/meps297131

Relationship between benthic foraminifera and food resources in South San Francisco Bay, California, USA

Amy E. Lesen*

Department of Integrative Biology and Museum of Paleontology, University of California, Berkeley, California 94720-3140, USA
Present address: Department of Math and Science, Pratt Institute, 200 Willoughby Avenue, Brooklyn, New York 11205, USA

ABSTRACT: Foraminifera are amongst the most abundant known protists found in marine habitats, and are ecologically important constituents of the benthic meiofauna. The seasonality of San Francisco Bay, USA, makes it an ideal system in which to study the relationships between primary production, organic matter fluxes, and food resources for the benthos. Samples were collected at one site at a depth of 8.8 m in South San Francisco Bay on monthly cruises for 2 yr from November 1999 through November 2001. Each month, water column parameters (chlorophyll concentration) and sediment parameters (chlorophyll, total organic carbon, nitrogen, amino acids, bacterial abundance) were measured, and benthic foraminiferal population size and biovolume was counted and calculated. Water column chlorophyll peaked in the spring of 2000 and 2001, and the fall of 2000, with sediment parameters peaking 1 to 3 mo later. The benthic foraminiferal standing crop peaked during the spring of both study years, and showed a large peak in the fall of 2001 dominated by the small-sized foraminifer Fursenkoina pontoni. The data strongly suggest that benthic foraminifera increase in number following phytoplankton blooms when many kinds of sediment organic matter also increase. Foraminiferal biovolume does not necessarily follow this pattern, especially when peaks in standing crop mainly consist of small-sized individuals. Foraminiferal biovolume and standing crop generally increase when the sediment C:N ratio increases, suggesting that benthic foraminiferal populations in South San Francisco Bay may be exploiting a detrital food source in addition to recently deposited fresh phytoplankton. Thus, foraminifera are probably quick to exploit sediment organic matter, and may be important remineralizers of nutrients in this system.

KEY WORDS: Benthic ecology · Foraminifera · Marine protists · Population dynamics · Food webs · Estuarine ecology · Meiofauna · Organic matter

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