Study on Potentially Toxic Benthic Dinoflagellate Assemblages on Dead Corals in Nha Trang Bay, Vietnam

Dead branching coral samples were collected in Nha Trang Bay to isolate benthic dinoflagellates. The identification and taxonomic observation of benthic dinoflagellates were based on cell size, shape, surface morphology, and thecal plate structure using light microscopy and scanning electron microscopy. A total of 27 benthic dinoflagellate species belonging to 5 orders were identified from dead corals. The cell density of dinoflagellates varied spatially. During the dry season, the highest density reached 17.8 cells/cm², while in the rainy season, the highest density was 15.7 cells/cm². Five species of Gambierdiscus australes, G. carpenteri, G. caribaeus, G. polynesiensis, G. belizeanus, which are known to cause Ciguatera Fish Poisoning (CFP), were also detected, although their cell densities were low, reaching 2.8 cells/cm² in the dry season and 0.5 cells/cm² in the rainy season.