Red tides and associated fisheries damage caused by the harmful raphidophyte Chattonella were reassessed based on the documented local records for 50 years to understand the distribution and economic impacts of the harmful species in the Western Pacific. Blooms of Chattonella with fisheries damage have been recorded in East Asia since 1969, whereas they have been only recorded in Southeast Asia since the 1980s. Occurrences of Chattonella have been documented from six Southeast Asian countries, Indonesia, Malaysia, Philippines, Singapore, Thailand and Viet Nam, with mass mortalities mainly of farmed shrimp in 1980-1990s, and farmed fish in 2000-2010s. These occurrences have been reported with the names of C. antiqua, C. marina, C. ovata, C. subsalsa and Chattonella sp., owing to the difficulty of microscopic species identification, and many were not supported with molecular data. To determine the distribution of C. marina complex and C. subsalsa in Southeast Asia, molecular phylogeny and microscopic observation were also carried out for cultures obtained from Indonesia, Malaysia, Japan, Philippines, Russia, Singapore and Thailand. The results revealed that only the genotype of C. marina complex has been detected from East Asia (China, Japan, Korea and Russia), whereas both C. marina complex (Indonesia and Malaysia) and C. subsalsa (Philippines, Singapore and Thailand) were found in Southeast Asia. Ejection of mucocysts has been recognized as a diagnostic character of C. subsalsa, but it was also observed in our cultures of C. marina isolated from Indonesia, Malaysia, Japan, and Russia. Meanwhile, the co-occurrences of the two harmful Chattonella species in Southeast Asia, which are difficult to distinguish solely based on their morphology, suggest the importance of molecular identification of Chattonella genotypes for further understanding of their distribution and negative impacts.

Morphological variation, ultrastructure, pigment composition and phylogeny of an oceanic, star-shaped, unarmored dinoflagellate Asterodinium gracile were examined using a culture established from Nagasaki, Japan, in 2017. Our examinations were based on LM, SEM, TEM, high-performance liquid chromatography (HPLC) and molecular phylogeny inferred from nuclear-encoded internal transcribed spacer (ITS) and 28S rDNA and chloroplast-encoded 16S rDNA sequences. Typical cells were stellate, possessing an apical, two lateral, and two antapical extensions. Cells ranged in size from 62.5 to 105.6 µm long and 21.2 to 39.5 µm in cingular width. The length and orientation of cellular extensions were variable; that is, two lateral extensions were usually symmetrically bent or retracted. Ellipsoidal cells without extensions were also observed. The apical structure complex was straight or slightly sigmoid. A spherical nucleus was located at the left side in the hyposome. The numerous discoid, yellowish-brown chloroplasts were variable in size and distributed also in the cell extensions. Among Kareniaceae, the lack of a pyrenoid in Asterodinium is unique. Nuclear-encoded ITS and 28S phylogenies suggested that A. gracile is closely related to Karenia papilionacea in the Kareniaceae, but its affinity to Brachidinium capitatum, another species with extensions, was unclear. A phylogeny of 16S rDNA showed that chloroplasts of A. gracile are related to other kareniaceans derived from a haptophyte. These chloroplasts were of the fucoxanthin type, composed of pigments similar to those in other Kareniaceae; however, the detection of 19′-hexanoyloxyfucoxanthin as a major carotenoid, the low amount of fucoxanthin, and lack of 19′-butanoyloxyfucoxanthin in A. gracile were unusual for the family.