Seasonal fluctuations in abundance and production of bacteria, and quantitative relation with heterotrophic microflagellates in northern Hiroshima bay, Seto inland sea [Japan]
1996
Imai, I. (Nansei National Fisheries Research Inst., Ono, Hiroshima (Japan)) | Yamaguchi, M.
From March 1984 through to September 1985, seasonal fluctuations in abundance and production of bacteria, and the quantitative relation with heterotrophic microflagellates were investigated at a station in northern Hiroshima Bay, Seto Inland Sea. The mean cell volume of bacteria measured by image analysis ranged between 0.074 and 0.115 mu-cubic-meter (mean of total measurements = 0.094 mu-cubic-meter, n = 1260). Bacteria measure with DAPI-staining and epifluorescence microscopy were 0.9 x 10(6) - 4.8 x 10(6) cells.ml(-1) in number and 7.6 - 40.4 mu-gC.l(-1) in biomass. Bacterial production determined by the FDC (frequency of dividing cells) method ranged between 5.5 and 63.3 mu-gC.l(-1).day(-1). The bacterial biomass and production were more abundant from May to October, and average 15% of the phytoplankton biomass and 25% of primary production. Respectively. Heterotrophic microflagellates (HMF) were 1.0 x 10(3) - 8.8 x 10(3) cells/ml(-1) in number and 1.8 - 21.1 mu-gC.l(-1) in biomass, and were more abundant from June to September. The mean ratios of HMF/bacteria were 1/613 in number and 0.47/1 in biomass, respectively. Grazing rates of HMF on bacteria estimated from HMF densities and water temperatures ranged between 0.007.h(-1) and 0.127.h(-1) with the higher rates in the summer. The ratio of the grazing rate to the bacterial growth rate (grazing/growth, %) was estimated to be 15% - 162% with a mean of 67%. It is inferred that bacteria utilized about a half of the primary production and then bacteria were vigorously grazed by HMF in the food webs of coastal seas such as Hiroshima Bay
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