Species Overview: Alexandrium tamarense is an armoured, marine, planktonic dinoflagellate. It is associated with toxic PSP blooms in cold water coastal regions.
Taxonomic Description: Cells of A. tamarense are small to medium in size, nearly spherical, and slightly longer than wide (Fig. 1). The first apical plate bears a ventral pore (Figs. 3, 5). Cells are commonly found single or in pairs (Figs. 1-3), and less commonly in fours. Paired cells may contain an anterior attachment pore (aap) and a posterior attachment pore (pap)(Fig. 4). Thecal plates are smooth and thin (Fig. 3). The size and shape of this species is highly variable: cells range in size between 22-51 Ám in length and 17-44 Ám in transdiameter width (Lebour 1925; Fukuyo et al. 1990; Hallegraeff 1991; Hallegraeff et al. 1991; Larsen & Moestrup 1989; Balech 1995; Taylor et al. 1995; Steidinger & Tangen 1996).
Thecal Plate Description: The plate formula for A. tamarense is: Po, 4', 6'', 6c, 8s, 5''', 2''''. The apical pore complex (APC) is rectangular and narrows ventrally (Fig. 3). The apical pore plate (Po) houses a large fishhook shaped foramen and a small round aap (Figs. 3, 4). The first apical plate (1') is variable in shape: from a broad triangle to a narrow rectangle, and bears a small ventral pore (Figs. 3, 5). The 1' plate comes in direct contact with the Po (Fig. 3) (Lebour 1925; Fukuyo et al. 1985; 1990; Larsen & Moestrup 1989; Balech 1995; Taylor et al. 1995; Steidinger & Tangen 1996).
Morphology and Structure: A. tamarense is a photosynthetic species with a number of orange-brown chloroplasts. A lunar-shaped nucleus is situated ventrally just inside the cingulum (Fig. 1) (Fukuyo 1985; Larsen & Moestrup 1989).
Reproduction: A. tamarense reproduces asexually by binary fission; plane of fission is oblique. This species also has a sexual cycle with anisogamous mating types. The gametes join laterally for sexual fusion, produce a planozygote which then encysts into a characteristic resting cyst (Fig. 6) (Loeblich & Loeblich 1975; Turpin et al. 1978; Silva 1962).
Ecology: A. tamarense is a planktonic dinoflagellate species associated with toxic paralytic shellfish poisoning (PSP) events around the world. Toxic blooms are commonly reported in Japan (Fukuyo et al. 1985; Ogata et al. 1982; Oshima et al. 1982). Red tide blooms of A. tamarense have been reported in Europe (Mortensen 1985; Moestrup & Hansen 1988), and are common along the NE coast of North America (New England and Canada) (Bicknell & Walsh 1975; Hurst 1975; Loeblich & Loeblich 1975). During a red tide event reported in the Faroe Islands, Norway, in 1984, population levels of A. tamarense were estimated at
1X 107 cells/L and completely dominated the plankton (Mortensen 1985; Moestrup & Hansen 1988).
Toxicity: Alexandrium tamarense is a known toxin-producing dinoflagellate species. This species produces very potent PSP neurotoxins which can affect humans, other mammals, fish and birds (Larsen & Moestrup 1989): gonyautoxins (GTX I, II, III, IV and V), neosaxitoxin (NSTX) and saxitoxin (SXT) (Shimizu et al. 1975; Oshima et al. 1977). This species is responsible for numerous human illnesses and several deaths after consumption of infected shellfish: ten deaths in Venezuela in 1977 (Reyes-Vasquez et al. 1979), and one death in Thailand in 1984 (Tamiyavanich et al. 1985). Resting cysts of A. tamarense can also harbor PSP toxins. Dale et al. (1978) demonstrated that cysts were more than ten times as toxic as their motile stage counterparts.
Species Comparison: A. tamarense can resemble a number of other species within the genus, but it can be distinguished by its cell shape and size, presence of a ventral pore (vp) on the 1' plate, and shape of the thecal plates (Balech 1995; Hallegraeff 1991; Larsen & Moestrup 1989; Steidinger & Tangen 1996).
Habitat and Locality: A. tamarense is a widely distributed coastal and estuarine dinoflagellate species (Lebour 1925; Steidinger & Tangen 1996) mainly found in cold to cold-temperate waters in North America, Europe and Japan. However, this species has been reported from warmer waters around the world: Australia, Venezuela and the Gulf of Thailand (Balech 1995; Fukuyo et al. 1990; Hallegraeff 1991; Steidinger & Tangen 1996; Taylor et al. 1995).