Toxigenic strains of Azadinium poporum (Amphidomataceae, Dinophyceae) from Japan and Vietnam, with first reports of A. poporum (ribotype A) and A. trinitatum in Asian Pacific

SUMMARY Morphology and phylogeny of small armored dinoflagellate Azadinium species isolated from Japanese and Vietnamese coasts were examined by light microscopy, scanning electron microscopy and molecular phylogeny inferred from ITS and LSU rDNA (D1–D3) sequences. Dominant azaspiracids (AZAs) were analyzed by using liquid chromatography/triple quadrupole mass spectrometer (LC/MS/MS). Sixteen and four culture strains were established from Japan and Vietnam, respectively. A phylogenetic tree confirmed our species identifications of Japanese cultures as Azadinium poporum (ribotypes A, B and C), A. trinitatum and A. zhuanum , and Vietnamese cultures as A. poporum (ribotype B). Typical cells of A. poporum had the thecal tabulation of Po, cp, X, 4′, 3a, 6″, 6C, 5S, 6″′, 2″″, A. trinitatum had Po, cp, X, 4–5′, 3a, 6–7″, 6C, 5S, 5–6″′, 2″″ and A. zhuanum had Po, cp, X, 3–4′, 2a, 6″, 6C, 5S, 6″′, 2″″. Cellular morphology of the three species were congruent with those in the original reports, in terms of the presence/absence of antapical spine and the position of the ventral pore, nucleus and pyrenoids, although small differences were also found in the nucleus position of A. trinitatum and A. zhuanum . AZA‐2 was the dominant component in Japanese A. poporum (ribotypes A, B and C), and AZA‐40 in Vietnamese A. poporum (ribotype B). AZA‐2 and AZA‐40 were not detected in Vietnamese and Japanese A. poporum , respectively. AZA analogs were not detected from A. trinitatum and A. zhuanum . This is the first report of the toxigenic A. poporum from Japan and Vietnam, with identifications of the major AZAs. The ribotype A of A. poporum and A. trinitatum were the first records in Asia.