Seasonal variations in abundance,growth and mortality of heterotrophic bacteria in Kagoshima Bay |
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| Authors: | Toru Kobari Tomo Fujii Yurie Kobari Akimasa Habano |
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| Institution: | (1) Marine Ecology, Dept. of Experimental Ecology, Leibnitz-Institut für Heereswissenschaften an der Universität Kiel, Düsternbrooker Weg 20, 24105 Kiel, Germany;(2) Dept. of Organismal Biology, Division of Ecology and Biodiversity, University of Salzburg, Hellbrunnerstr. 34, 5020 Salzburg, Austria;(3) Present address: Dept. of Organismal Biology, Division of Ecology and Biodiversity, University of Salzburg, Hellbrunnerstr. 34, 5020 Salzburg, Austria |
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| Abstract: | Seasonal changes in abundance, growth and mortality of heterotrophic bacteria were investigated monthly from collections and
dilution experiments in Kagoshima Bay, the southernmost of Japan. Bacteria occurred abundantly with considerable variation
in the surface layers where chlorophyll a concentrations were high, whereas seasonal variations were obscure below 100 m. Especially, bacteria showed a decline of
cell density toward summer when heterotrophic nano-flagellates increased their abundance. Seasonal and vertical variations
in bacterial cell number during the study period were positively correlated with those of water temperature and pico-sized
chlorophyll a concentration. Maximum growth and mortality rates showed positive correlations with water temperature but no positive relationships
to size-fractionated chlorophyll a. Net increase rate (i.e. in situ rate if abundance changes) was negatively correlated with cell density of heterotrophic nano-flagellates. It is concluded
that bacterial abundance is controlled by the resultant (i.e. net growth rate) of the balance between maximum growth and predatory
mortality by heterotrophic nano-flagelllates which are both dependent on ambient temperature. |
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