Reprint Series No. 24

BACTERIAL PRODUCTION AND CONSUMPTION IN MICROLAYER AND SUBSURFACE WATERS OF PADILLA BAY, WASHINGTON

Karen M. Thompson

August 1995

Bibliographic Citation
Thompson, Karen M. 1995. Bacterial production and consumption in microlayer and subsurface waters of Padilla Bay, Washington. Master of Science Thesis, Western Washington University, Bellingham, Washington. 82 pp. Washington State Department of Ecology (Publication No. SWR-95-76) Padilla Bay National Estuarine Research Reserve Reprint Series No. 24.

Abstract
Bacterial numbers, bacterial production and protistan bacterivory were measured in microlayer (- 100 µm) and subsurface (-25 cm) water in Padilla Bay, Washington. Objectives were to compare bacterial numbers and heterotrophic activity in microlayer and subsurface waters, and to investigate the fate of bacterial production. Bacterial abundance was higher in microlayers than in subsurface waters. In contrast, subsurface bacterial communities were metabolically more active than microlayer communities. Bacterial production in the microlayer may have been limited by substrate composition or inhibited by pollutants concentrated in the surface film. Differences in grazing pressure may also explain lower metabolic activity in microlayers. Heterotrophic activity in microlayers can exceed subsurface activity if enrichment of bacteria in the surface film is significant. Small flagellates <5 µm were the most abundant members of the heterotrophic protistan community in both the microlayer and the subsurface. Other heterotrophic protists included flagellates 5 to 20 µm, dinoflagellates, and ciliates. Bacterivory occurred in both microlayer and subsurface waters and was attributed largely to flagellates. Grazing rates were not equivalent to rates of bacterial cell production, and usually were less than 1% of the estimated bacterial cell production. It appears that bacterivory by heterotrophic protists is not a major path of energy transfer in microlayer or subsurface waters of Padilla Bay. Other factors may be more important in balancing bacterial growth, such as physical advection and viral lysis.