Occurrence of parasitic infections in a Margalefidinium polykrikoides (Dinophyceae) bloom in the Taiwan Strait in 2018

Abstract

The harmful dinoflagellate species Margalefidinium polykrikoides is comprised of several ribotypes and is responsible for recurrent blooms worldwide. Parasitic dinoflagellates have been suggested to play a role in the decline of M. polykrikoides blooms; however, information on the host–parasite interaction remains limited. We report a bloom caused by M. polykrikoides ribotype I in the Taiwan Strait in June 2018, as confirmed by microscopic observation and molecular characterization. Amoebophrya ceratii infecting M. polykrikoides was identified by single-cell polymerase chain reaction and subsequent direct sequencing of the LSU rRNA gene from the bloom samples, which shared a 94.72% similarity with Amoebophrya ceratii ex Levanderina fissa. DNA metabarcoding targeting SSU rRNA genes of the V4 region revealed a high diversity of Amoebophrya infecting various hosts in the bloom samples. Amoebophrya ceratii accounted for approximately 45% of Syndiniales Group II from the bloom samples, but less than 2.5% in the non-bloom samples. In addition to two known Amoebophrya spp. ex M. polykrikoides from South Korea, our results provide evidence of infection of M. polykrikoides by a third Amoebophrya species; however, its exact role in the bloom decline of M. polykrikoides remains to be determined.