Spreading Mechanism of Harmful Red Tides in WESTPAC Area

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Cooperative research among scientists in Japan and western Pacific countries, especially Southeast Asia, was conducted in order to clarify the current situation of distribution of toxic plankton, which caused toxin contamination in fish and shellfish, with emphasis on elucidation of mechanism of their geographical expansion. The research result revealed that causative organisms responsible for paralytic shellfish poisoning (PSP), Pyrodinium bahamense, Gymnodinium catenatum, and Alexandrium spp. occurred widely in tropical waters. Two dinoflagellates possibly responsible for diarrhetic poisoning (DSP), Dinophysis caudata and D.miles were also found commonly in tropical waters. A diatoms responsible for amnesic poisoning (ASP) Pseudo-nitzschia spp. were also distributed widely, but any toxin contamination had not been confirmed yet. Distribution of these toxic species looks wider and wider, as research was conducted in new area, although it was not clear whether the species invaded from other place recently or stayed the same area for a long time.In the Philippines, where damage caused by PSP is most serious in the world, the distribution of P.bahamense was expanding to south to Mindanao Island. The same species was found in Saba, Malaysia where water current reach from Mindanao. Other PSP species, G.catenatum and Alexandrium sp. were also found in the Philippine waters. Using plankton samples collected from Panay Island, DSP toxin productivity of D.caudata and D.miles was confirmed for the first time in tropical dinoflagellates.In Vietnam, where the occurrence of toxic plankton was denied before the present research, four Alexandrium species (A.andersonii, A.insuetwn, A.minutum, A.tamiyavanichii) were found in coastal waters and shrimp culture ponds. PSP toxin productivity of A.minutum was confirmed using an unialgal culture. ASP toxicity was found in benthic diatom, Nitzschia sp, isolated from shrimp culture pond.