Harmful Algae 1 (2002) 265–275 Alexandrium (Dinophyceae) species in Malaysian waters Gires Usup a,∗ , Leaw Chui Pin a , Asmat Ahmad a , Lim Po Teen b a Program Sains Laut, Pusat Pengajian Sains Sekitaran dan Sumber Alam, Fakulti Sains dan Teknologi, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia b Fakulti Sains dan Teknologi Sumber, Universiti Malaysia Sarawak, 94300 Kota Samarahan, Sarawak, Malaysia Received 8 July 2002; received in revised form 2 August 2002; accepted 22 August 2002 Abstract A study was carried out to determine the presence of paralytic shellfish poisoning (PSP) toxin-producing dinoflagellates in the coastal waters of Peninsula Malaysia. This followed first ever occurrences of PSP in the Straits of Malacca and the northeast coast of the peninsula. The toxic tropical dinoflagellate Pyrodinium bahamense var. compressum was never encountered in any of the plankton samples. On the other hand, five species of Alexandrium were found. They were Alexandrium affine, Alexandrium leei, Alexandrium minutum, Alexandrium tamarense and Alexandrium tamiyavanichii. Not all species were present at all sites. A. tamiyavanichii was present only in the central to southern parts of the Straits of Malacca. A. tamarense was found in the northern part of the straits, while A. minutum was only found in samples from the northeast coast of the peninsula. A. leei and A. affine were found in both the north and south of the straits. Cultured isolates of A. minutum and A. tamiyavanichii were proven toxic by the receptor binding assay for PSP toxins but A. tamarense clones were not toxic. Mean toxin content for the A. tamiyavanichii and A. minutum clones were 26 and 15fmol per cell STX equivalent, respectively. This study has provided evidence on the presence of PSP toxin-producing Alexandrium species in Malaysian waters which suggests that PSP could increase in importance in the future. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Alexandrium; Harmful algal blooms; Malaysia; Paralytic shellfish poisoning 1. Introduction Malaysia is one of many countries affected by harm- ful algal blooms (HABs) and associated seafood poi- soning. Currently, paralytic shellfish poisoning (PSP) is the only HAB-related shellfish poisoning that has been documented in the country. Until 1990, PSP was confined to the west coast of Sabah, where the di- noflagellate Pyrodinium bahamense Plate var. com- pressum Böhm form blooms almost annually. This ∗ Corresponding author. Tel.: +60-3-89213219; fax: +60-3-89253357. E-mail address: gires@pkrisc.cc.ukm.my (G. Usup). species has long been considered the most impor- tant PSP toxin-producing species in southeast Asia (Malaysia and The Philippines) and along the Pacific coastline of central America (Rosales-Loessener et al., 1989; Orellana-Cepeda et al., 1998; Usup and Azanza, 1998). In Malaysia alone, P. bahamense has caused many poisoning events including several fatalities. In early 1991, PSP occurred for the first time out- side Sabah. Three people were poisoned after con- suming mussels from a mussel farm in Sebatu in the Straits of Malacca. Naturally P. bahamense was sus- pected to be the toxin producer, but to date the species has never been found in plankton samples collected from several locations in the Straits of Malacca. In the 1568-9883/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S1568-9883(02)00044-6