title: Feeding and grazing impact by small marine heterotrophic dinoflagellates on heterotrophic bacteria.
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 x 10(6) 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.
authors.affiliation: School of Earth and Environmental Sciences, College of Natural Sciences, Seoul National University, Seoul 151-747, Korea. hjjeong@snu.ac.kr
authors.forename: Hae Jin
authors.initials: HJ
authors.lastname: Jeong
authors.forename: Kyeong Ah
authors.initials: KA
authors.lastname: Seong
authors.forename: Yeong Du
authors.initials: YD
authors.lastname: Yoo
authors.forename: Tae Hoon
authors.initials: TH
authors.lastname: Kim
authors.forename: Nam Seon
authors.initials: NS
authors.lastname: Kang
authors.forename: Shin
authors.initials: S
authors.lastname: Kim
authors.forename: Jae Yeon
authors.initials: JY
authors.lastname: Park
authors.forename: Jae Seong
authors.initials: JS
authors.lastname: Kim
authors.forename: Gwang Hoon
authors.initials: GH
authors.lastname: Kim
authors.forename: Jae Yoon
authors.initials: JY
authors.lastname: Song
mesh_terms: D000818:Animals; D001419:Bacteria; D046169:Dermoscopy; D004141:Dinoflagellida / Q000382:microbiology* / Q000648:ultrastructure; D007723:Korea; D046529:Microscopy, Electron, Transmission; D020045:Pfiesteria piscicida / Q000382:microbiology / Q000648:ultrastructure; D011235:Predatory Behavior / Q000502:physiology; D014871:Water Microbiology