Aquatic Sciences Meeting, Albuquerque 2001
| CS20 Microbial Dynamics |
| Date: Friday, February 16, 2001, Time: 9:00:00 AM |
| Location: Ruidoso/Pecos |
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| Landry, M, R, Dept. Oceanogr., Univ. Hawaii at Manoa, Honolulu, USA, landry@soest.hawaii.edu |
| Calbet, A, , Inst. Cičncies del Mar, CSIC, Barcelona, Spain, acalbet@icm.csic.es |
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| BACTERIA-FLAGELLATE INTERACTIONS IN OLIGOTROPHIC WATERS OF THE SUBTROPICAL NORTH PACIFIC |
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| The number and relative strenghts of trophic linkages in the microbial community of the oligotrophic Subtropical North Pacific were studied experimentally from August 1998 to April 1999 at Stn. ALOHA (100 km north of Oahu, Hawaii). Collected seawater was manipulated by sequential size-fractionation to truncate the food web at different organism sizes (1, 2, 5, 10 and 20 µm), and the response variable, net bacterial growth rate, was assessed from flow cytometric analyses of the changes in cell abundance. The corresponding size structure of the protistan grazer assemblage was measured microscopically. Bacteria displayed somewhat lower temporal variability in abundance than nanoflagellates. Despite the semblance of relative constancy, however, microbial community interactions varied markedly among the experiments. For experiments conducted with relatively high bacterial biomass compared to Hflag, the bacteria showed little growth response to the removal of predators and may have been resource limited. When conditions were defined by relatively low bacterial biomass and high Hflag biomass, a depression of net growth in the smallest size fraction (<1 µm) compared to the <2µm fraction suggested selection for smaller bacterivores. At intermediate conditions, where the biomass ratio of bacteria to Hflag was transitioning from higher to lower values, the growth dynamics of bacteria were marked by significant cascade influences among the different size fractions. These results may be features of a regular oscillatory pattern that regulates open-ocean microbial populations at different temporal and spatial scales. In such oscillations, the indirect influences of a protistan predatory chain can tip the balance between resource limitation and predatory control. |
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