Journal
ALGAE
Volume 32, Issue 1, Pages 47-55Publisher
KOREAN SOC PHYCOLOGY
DOI: 10.4490/algae.2017.32.3.8
Keywords
bacterivory; grazing; Mesodinium; protist; red tide
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Funding
- National Research Foundation of Korea (NRF) grants - Korea government (MSIP) [NRF-2015-M1A5A1041808, NRF-2016-R1D1A3B03931620, NRF-2016-R1C1B1007340]
- Management of marine organisms causing ecological disturbance and harmful effect Program of Korea Institute of Marine Science and Technology Promotion (KIMST)
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We explored feeding by the mixotrophic ciliate Mesodinium rubrum, heterotrophic nanoflagellates (HNFs), and small ciliates (< 30 mu m in cell length) on natural populations of heterotrophic bacteria in Masan Bay, Keum River Estuary, and in the coastal waters of the Saemankeum area, Korea when M. rubrum red tides occurred. We also measured ingestion rates of M. rubrum on cultured heterotrophic bacteria as a function of bacterial concentration in the laboratory. The ingestion rates of M. rubrum on natural populations of heterotrophic bacteria (2.3-16.8 bacteria grazer(-1) h(-1)) were comparable to or lower than those of co-occurring HNFs (10.7-41.7 bacteria grazer(-1)h(-1)), but much lower than those of co-occurring small ciliates (76.0-462.2 bacteria grazer(-1) h(-1)). However, the maximum grazing coefficient of M. rubrum (0.245 d(-1)) on natural populations of heterotrophic bacteria was much higher than that of small ciliates (0.089 d(-1)), and slightly higher than that of HNFs (0.204 d(-1)). With increasing bacterial concentrations, ingestion rates of M. rubrum on cultured heterotrophic bacteria continuously increased, but became saturated at higher prey concentrations over 1-5 x 10(6) cells mL(-1). The maximum ingestion rate of M. rubrum on cultured heterotrophic bacteria was 34.4 bacteria grazer(-1) h(-1). Based on the present study, it is suggested that M. rubrum maybe an important grazer of heterotrophic bacteria and sometimes have considerable grazing impact on natural populations of heterotrophic bacteria.
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