Marine epibenthic dinoflagellates have been collected from macroalgae, dead corals, seagrasses and sand in Malaysia and identified using light microscopy, including epifluorescence microscopy, and scanning electron microscopy. Examination of 62 samples revealed that Malaysia has rich diversity of benthic dinoflagellates, with 24 species representing 9 genera. Of these species, 8 were shown to be potentially toxic using the Anemia bioassay test i.e. Prorocentrum arenarium, P. lima, P. concavum, P. cf. faustiae, Gambierdiscus pacificus, Ostreopsis labens, O. ovata and Coolia sp. The diversity of potentially toxic species in Malaysian waters indicates that Malaysia may encounter problems with ciguatera and/or DSP. The highest species diversity was found at Sipadan Island with a total of 18 species identified. One of these is previously undescribed (Prorocentrum sipadanensis sp. nov.). The most common species identified at all sampling sites were Prorocentrum lima and Ostreopsis ovata. Generally, the morphology of the species identified from Malaysian waters is similar to that reported in studies elsewhere. However, new features were also observed (e.g. a pyrenoid in Prorocentrum emarginatum and two different‐sized pores in Ostreopsis labens). The importance of SEM as a tool in taxonomic studies is stressed.

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Harmful algal blooms (HABs) resulting in red discoloration of coastal waters in Sepanggar Bay, off Kota Kinabalu, Sabah, East Malaysia, were first observed in January 2005. The species responsible for the bloom, which was identified as Cochlodinium polykrikoides, coincided with fish mortalities in cage-cultures. Determinations of cell density between . Cell abundance reached a maximum value of 6 Â 10 6 cells L À1 at the fish cage sampling station where the water quality was characterized by high NO 3 -N and PO 4 -P concentrations. These blooms persisted into August 2005, were not detected during the north-east monsoon season and occurred again in May 2006. Favorable temperature, salinity and nutrient concentrations, which were similar to those associated with other C. polykrikoides blooms in the Asia Pacific region, likely promoted the growth of this species. Identification of C. polykrikoides as the causative organism was based on light and scanning microscopy, and confirmed by partial 18S ribosomal DNA sequences of two strains isolated during the bloom event (GenBank accession numbers DQ915169 and DQ915170). #