Ingestion of the unicellular cyanobacterium <i>Synechococcus</i> by the mixotrophic red tide ciliate <i>Mesodinium rubrum</i>

doi:2015.30.4.281

Algae > Volume 30(4); 2015 > Article

Algae 2015;30(4): 281-290. doi: https://doi.org/10.4490/algae.2015.30.4.281

Ingestion of the unicellular cyanobacterium Synechococcus by the mixotrophic red tide ciliate Mesodinium rubrum

Yeong Du Yoo¹, Kyeong Ah Seong², Geumog Myung¹, Hyung Seop Kim¹, Hae Jin Jeong³, Brian Palenik⁴ and Wonho Yih¹^,*

¹Department of Marine Biotechnology, College of Ocean Science and Technology, Kunsan National University, Kunsan 54150, Korea
²Converging Research Division, National Marine Biodiversity Institute of Korea, Chungnam 33662, Korea
³School of Earth and Environmental Sciences, College of Natural Sciences, Seoul National University, Seoul 08826, Korea
⁴Marine Biology Research Division, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA 92093-0202, USA

*Corresponding Author

Email: ywonho@kunsan.ac.kr

ABSTRACT

We explored phagotrophy of the phototrophic ciliate Mesodinium rubrum on the cyanobacterium Synechococcus. The ingestion and clearance rates of M. rubrum on Synechococcus as a function of prey concentration were measured. In addition, we calculated grazing coefficients by combining the field data on abundance of M. rubrum and co-occurring Synechococcus spp. with laboratory data on ingestion rates. The ingestion rate of M. rubrum on Synechococcus sp. linearly increased with increasing prey concentrations up to approximately 1.9 × 106 cells mL-1, to exhibit sigmoidal saturation at higher concentrations. The maximum ingestion and clearance rates of M. rubrum on Synechococcus were 2.1 cells predator-1 h-1 and 4.2 nL predator-1 h-1, respectively. The calculated grazing coefficients attributable to M. rubrum on cooccurring Synechococcus spp. reached 0.04 day-1. M. rubrum could thus sometimes be an effective protistan grazer of Synechococcus in marine planktonic food webs. M. rubrum might also be able to form recurrent and massive blooms in diverse marine environments supported by the unique and complex mixotrophic arrays including phagotrphy on hetrotrophic bacteria and Synechococcus as well as digestion, kleptoplastidy and karyoklepty after the ingestion of cryptophyte prey.

Key words: grazing impact; ingestion; Mesodinium; mixotrophy; Synechococcus