Differential predation by common heterotrophic protists on four species of the dinoflagellate genus Scrippsiella

Dinoflagellates are ubiquitous in marine environment and play diverse roles in marine ecosystems. The dinoflagellate genus Scrippsiella sometimes causes red tides. To understand the population dynamics of a Scrippsiella species, mortality due to predation should be explored. However, predation by heterotrophic protists on only a few Scrippsiella species has been investigated. Thus, feeding by common heterotrophic dinoflagellates Gyrodinium dominans, Pfiesteria piscicida, Polykrikos kofoidii, Oblea rotunda, Oxyrrhis marina, and the ciliate Strombidinopsis sp. on four Scrippsiella species having similar size, which are S. acuminata, S. donghaiensis, S. lachrymosa, and S. masanensis, was explored. All heterotrophic predators were able to feed on four Scrippsiella species. However, the growth and ingestion rates of P. kofoidii on four Scrippsiella species were different. With increasing mean prey concentrations, growth and ingestion rates of P. kofoidii on S. lachrymosa increased rapidly, and saturated similar to those on S. acuminata, however, those of on S. donghaiensis decreased continuously because S. donghaiensis lysed cells of P. kofoidii. In contrast, the growth and ingestion rates of P. kofoidii on S. masanensis were not significantly affected by prey concentrations. At comparable high mean prey concentrations, growth and ingestion rates of G. dominans were different significantly between four Scrippsiella species. Therefore, differences in the growth and/or ingestion rates of some heterotrophic protists on the four Scrippsiella species might result in different ecological niches of both the predator and prey species and affect causative species of red tides.