Ecological survey on a dinoflagellate possibly responsible for the induction of ciguatera

Following the previous discovery of a new toxic dinoflagellate Gambierdiscus toxicus as the most likely cause of ciguatera, an ecological survey was undertaken on this organism around Tahiti Island and in the Gambier Islands of French Polynesia. In the survey the epiphytic nature of the dinoflagellate was disclosed and a rapid assay method was established by taking advantage of this living patten. The method consisted of shaking off of the organisms from the appropriate substrative algae and subsequent microscopic counting of the cells. The population of the organism was found much higher in the Gambier Islands than around Tahiti, even though there were marked regionalities in both survey areas. The distribution map prepared by the survey not only agreed well with the results of the past surveys but gave a more quantitiative and clearer picture of the ciguatera-endemicity of the areas.