AUTHOR=Park Sang Ah , Jeong Hae Jin , Ok Jin Hee , Kang Hee Chang , You Ji Hyun , Eom Se Hee , Park Eun Chong 

TITLE=Interactions Between the Kleptoplastidic Dinoflagellate Shimiella gracilenta and Several Common Heterotrophic Protists

JOURNAL=Frontiers in Marine Science

VOLUME=8

YEAR=2021

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2021.738547

DOI=10.3389/fmars.2021.738547

ISSN=2296-7745

ABSTRACT=<p>The newly described dinoflagellate, <italic>Shimiella gracilenta</italic>, is known to survive for approximately 1 month on the plastids of ingested prey cells during starvation, indicating kleptoplastidy. To understand the population dynamics of this dinoflagellate in marine planktonic food webs, its growth and mortality rate due to predation should be assessed. Thus, we investigated the feeding occurrence of eight common heterotrophic protists on <italic>S. gracilenta</italic>. We also determined the growth and ingestion rates of <italic>Oxyrrhis marina</italic> and the naked ciliate, <italic>Rimostrombidium</italic> sp. on <italic>S. gracilenta</italic> as a function of the prey concentration. The common heterotrophic dinoflagellates (HTDs) <italic>Gyrodinium dominans, O. marina</italic>, and <italic>Pfiesteria piscicida</italic> and a naked ciliate <italic>Rimostrombidium</italic> sp. were able to feed on <italic>S. gracilenta</italic>; whereas the HTDs <italic>Aduncodinium glandula, Gyrodinium jinhaense, Oblea rotunda</italic>, and <italic>Polykrikos kofoidii</italic> were not. <italic>Shimiella gracilenta</italic> supported positive growth of <italic>O. marina</italic> and <italic>Rimostrombidium</italic> sp. but did not support that of <italic>G. dominans</italic> and <italic>P. piscicida</italic>. With increasing prey concentrations, the growth and ingestion rates of <italic>O. marina</italic> and <italic>Rimostrombidium</italic> sp. on <italic>S. gracilenta</italic> increased and became saturated. The maximum growth rates of <italic>O. marina</italic> and <italic>Rimostrombidium</italic> sp. on <italic>S. gracilenta</italic> were 0.645 and 0.903 day<sup>−1</sup>, respectively. Furthermore, the maximum ingestion rates of <italic>O. marina</italic> and <italic>Rimostrombidium</italic> sp. on <italic>S. gracilenta</italic> were 0.11 ng C predator day<sup>−1</sup> (1.6 cells predator<sup>−1</sup> day<sup>−1</sup>) and 35 ng C predator day<sup>−1</sup> (500 cells predator<sup>−1</sup> day<sup>−1</sup>), respectively. The maximum ingestion rate of <italic>O. marina</italic> on <italic>S. gracilenta</italic> was lower than that on any other algal prey reported to date, although its maximum growth rate was moderate. In conclusion, <italic>S. gracilenta</italic> had only a few common heterotrophic protist predators but could support moderate growth rates of the predators. Thus, <italic>S. gracilenta</italic> may not be a common prey species for diverse heterotrophic protists but may be a suitable prey for a few heterotrophic protists.</p>