AME 23:263-271 (2001)  -  doi:10.3354/ame023263

Bacterial abundance and production and heterotrophic nanoflagellate abundance in subarctic coastal waters (Western North Pacific Ocean)

Choon Weng Lee*, Isao Kudo, Mitsuru Yanada, Yoshiaki Maita

Laboratory of Marine Environmental Science, Graduate School of Fisheries Science, Hokkaido University, 3-1-1 Minato, Hakodate, 041-8611 Japan

ABSTRACT: We studied the temporal variations of bacterial abundance and production in subarctic Funka Bay (Hokkaido, Japan) for a 1 yr period, and related this data to chlorophyll a (chl a) concentration (highest conc. = 5.9 μg l-1), particulate organic carbon (POC) concentration (ranging from 60 to 360 μg C l-1), heterotrophic nanoflagellate (HNF) abundance (<0.5 to 5.6 x 103 cells ml-1), and temperature. Bacterial abundance ranged from 2.6 to 9.1 x 105 cells ml-1, whereas bacterial production ranged from 0.1 to 22.9 μg C l-1 d-1. The calculated bacterial growth rate ranged from 0.02 to 2.57 d-1, with an average turnover time of 1.6 d, and Œattached¹ bacteria (>1 μm fraction) contributed more than half the total bacterial production (mean ± 95% CL = 54 ± 12%). Bacterial abundance was relatively stable throughout the year (coefficient of variation, CV = 20%) even though the CV for bacterial production was high (CV = 100%). Grazing (top-down) is an important control mechanism in Funka Bay, and HNF seemed to be directly cropping bacterial production. Annual bacterial production was estimated at 140 g C m-2 yr-1, and was relatively high compared to the annual primary production (100 to 170 g C m-2 yr-1), indicating the importance of the microbial loop in Funka Bay. After bacterial respiration loss was accounted for, bacterial carbon demand was higher than primary production. The inflow of Tsugaru warm water, a branch of the Kuroshio Current brought organic matter, but the concentration of POC and the timing of the inflow suggested that this organic matter addition was insignificant, and we concluded that other sources, including riverine input, are more important sources of organic matter.

KEY WORDS: Bacterial production · Funka Bay · Heterotrophic nanoflagellate · Particulate organic matter · Tsugaru warm water

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