Feeding and grazing impact by small marine heterotrophic dinoflagellates on heterotrophic bacteria |
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Authors: | Jeong Hae Jin Seong Kyeong Ah Yoo Yeong Du Kim Tae Hoon Kang Nam Seon Kim Shin Park Jae Yeon Kim Jae Seong Kim Gwang Hoon Song Jae Yoon |
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Institution: | School of Earth and Environmental Sciences, College of Natural Sciences, Seoul National University, Seoul 151-747, Korea, and; Department of Oceanography, College of Ocean Science and Technology, Kunsan National University, Kunsan 573-701, Korea, and; Red Tide Research Center, College of Ocean Science and Technology, Kunsan National University, Kunsan 573-701, Korea, and; Department of Biology, College of Natural Sciences, Kongju National University, Kongju 314-701, Korea |
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Abstract: | ABSTRACT. We investigated the feeding of the small heterotrophic dinoflagellates (HTDs) Oxyrrhis marina , Gyrodinium cf. guttula , Gyrodinium sp., Pfiesteria piscicida , and Protoperidinium bipes on marine heterotrophic bacteria. To investigate whether they are able to feed on bacteria, we observed the protoplasm of target heterotrophic dinoflagellate cells under an epifluorescence microscope and transmission electron microscope. In addition, we measured ingestion rates of the dominant heterotrophic dinoflagellate, Gyrodinium spp., on natural populations of marine bacteria (mostly heterotrophic bacteria) in Masan Bay, Korea in 2006–2007. Furthermore, we measured the ingestion rates of O. marina , G . cf. guttula , and P. piscicida on bacteria as a function of bacterial concentration under laboratory conditions. All HTDs tested were able to feed on a single bacterium. Oxyrrhis marina and Gyrodinium spp. intercepted and then ingested a single bacterial cell in feeding currents that were generated by the flagella of the predators. During the field experiments, the ingestion rates and grazing coefficients of Gyrodinium spp. on natural populations of bacteria were 14–61 bacteria/dinoflagellate/h and 0.003–0.972 day−1, respectively. With increasing prey concentration, the ingestion rates of O. marina , G . cf. guttula , and P. piscicida on bacteria increased rapidly at prey concentrations of ca 0.7–2.2 × 106 cells/ml, but increased only slowly or became saturated at higher prey concentrations. The maximum ingestion rate of O. marina on bacteria was much higher than those of G . cf. guttula and P. piscicida . Bacteria alone supported the growth of O. marina . The results of the present study suggest that some HTDs may sometimes have a considerable grazing impact on populations of marine bacteria, and that bacteria may be important prey. |
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Keywords: | Bacterivory feeding behavior food web graze ingestion microbial loop protist |
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