Characterization of G ambierdiscus and C oolia ( D inophyceae) isolates from T hailand based on morphology and phylogeny

Summary The benthic dinoflagellates in the genus G ambierdiscus produce toxins that bioaccumulate in tropical and sub‐tropical fish causing ciguatera fish poisoning ( CFP ). Other co‐occurring genera such as C oolia have also been implicated in causing CFP . Little is known about the diversity of the two genera G ambierdiscus and C oolia along the Thai coasts. The results of morphological analyses based on observation under light microscopy and scanning electron microcopy showed that strains of G ambierdiscus from T hailand displayed the typical G ambierdiscus plate formula: P o, 4′, 0a, 6″, 6c,?s, 5′′′, 0p and 2′′′′. Morphological examination of Thai G ambierdiscus enabled it to be identified as G ambierdiscus caribaeus : round and anterior‐posteriorly compressed cell shape, broad 2′′′′ plate, rectangular 2′ plate, and symmetrical 3″ plate. The phylogenetic analyses based on the large subunit ( LSU) rDNA D 8/ D 10 sequences of Gambierdiscus from T hailand confirmed the morphological identification. The thecal plate formula for all of the Coolia isolates from T hailand was P o, 4′, 0a, 6″,?c,?s, 5′′′, 0p and 2′′′′. Most, but not all, of these isolates could be identified morphologically as C oolia malayensis . An LSU rDNA D 1/ D 2 phylogenetic analysis confirmed identity of C . malayensis isolates identified morphologically. The remaining unidentified isolates fell in the C . tropicalis clade.