Here the occurrence of the species Gambierdiscus yasumotoi is reported for the first time along a latitudinal gradient spanning more than 1550. km of the Australian Great Barrier Reef (GBR), a region with endemic ciguatera fish poisoning. G. yasumotoi was found at three tropical and sub tropical coral reef sites, Raine Island (northern GBR), Nelly Bay (central GBR) and Heron Island (southern GBR), indicating a wide-ranging distribution in tropical and subtropical eastern Australia. Specimens from Australia broadly fitted the original description of G. yasumotoi, but differed in some aspects, showing some similarities to Gambierdiscus ruetzleri. Molecular phylogenetic analyses based on nuclear rRNA gene sequences and morphological analyses showed specimens to be intermediate between the two species G. yasumotoi and G. ruetzleri. The full intraspecific diversity of these two species appears to be incompletely known, and these two species may represent a species complex. Strains of this species from other sites around the world have been found to produce an as yet unknown toxin, possibly an analogue of maitotoxin.