Species of the marine dinoflagellate genus Karenia are known to produce various potent biotoxins and can form noxious blooms that cause mass mortalities of fish and shellfish. To date, harmful blooms of the species K. mikimotoi have been reported in Korea, but K. papilionacea was recently recorded off the southern coast of Korea. Here, we developed a quantitative real-time PCR (qRT-PCR) assay with specific primer pairs for the accurate detection and quantification of these two similar-looking unarmored species, K. mikimotoi and K. papilionacea, and investigated their distribution and dynamics in Korean coastal waters. Overall, K. papilionacea had not only a wider distribution, but also higher cell abundances (15–2553 cells L⁻¹) than K. mikimotoi (3–122 cells L⁻¹) in surface waters. Of 18 sampling sites, the two Karenia species were found to coexist at two sites. During monitoring at a fixed station (S5), K. papilionacea was generally predominant over K. mikimotoi; however, the two species exhibited similar dynamics and occasionally co-occurred. Both Karenia species showed similar physiological responses to temperature and salinity, requiring similar conditions for optimum growth. These results suggest that blooms of the two species may co-occur and induce a synergistic adverse effect on marine environments.

In the era of climate changes, harmful dinoflagellate outbreaks that produce potent algal toxins, odor, and water discoloration in aquatic environments have been increasingly reported. Thus, various treatments have been attempted for the mitigation and management of harmful blooms. Here, we report engineered nanoparticles that consist of two different types of rylene derivatives encapsulated in polymeric micelles. In addition, to avoid dissociation of the aggregate, the core of micelle was stabilized via semi-interpenetrating network (sIPN) formation. On two types of the marine red-tide dinoflagellates, Akashiwo sanguinea and Alexandrium pacificum, the nanoparticle uptake followed by fluorescence labeling and photothermal effect was conducted. Firstly, fluorescence microscopy enabled imaging of the dinoflagellates with the ultraviolet chromophore, Lumogen Violet. Lastly, near-infrared (NIR) laser irradiation was exposed on the Lumogen IR788 nanoparticle-treated Ak. Sanguinea. The irradiation resulted in reduced cell survival due to the photothermal effect in microalgae. The results suggested that the nanoparticle, IR788-sIPN, can be applied for potential red-tide algal elimination.

The syndinean genus Amoebophrya comprises endoparasitic dinoflagellates that infect various marine protists. Since the description of the type species, A. sticholonchae, a parasite of the radiolarian Sticholonche zanclea , an additional six Amoebophrya species have been formally described. Over the past 2 decades, intensive high‐throughput environmental sequencing has discovered widespread and extensive diversity of novel marine alveolate group II (MALV II), generally considered the Amoebophryidae. Of the large number of uncultured environmental sequences, only several clades of MALV II are associated with a few sequences representing the Amoebophrya ceratii complex (ACC) infecting free‐living dinoflagellates. In this study, we examined developmental traits and molecular signatures of A. sticholonchae and nine members of the ACC infecting diverse dinoflagellates from Korean coastal waters. Molecular phylogeny inferred from 18S rRNA gene sequences revealed that A. sticholonchae clustered with radiolarian‐associated sequences, forming a basal lineage to the ACC, which comprised eight distinct clades (ACC1–8). Developmental traits were phylogenetically structured. Of the eight clades, ACC1–4 infected host nuclei and lacked temporary polyploidy, except that cytoplasmic infection occurred in Karlodinium veneficum cells containing multiple parasites; ACC5 and ACC8 exhibited cytoplasmic infection with temporary polyploidy, except for Prorocentrum micans , showing a similar frequency of cytoplasmic and nuclear infections, and ACC6–7 showed nuclear infection accompanied by temporary polyploidy. In contrast, A. sticholonchae uniquely combined cytoplasmic infection with the absence of temporary polyploidy. Although complex, these results suggest that phylogenetic divergence of the ACC group is generally consistent with developmental stage‐specific characteristics, which is potentially useful in future taxonomic classification of this diverse lineage.