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Alexandrium tamarense (Lebour) Balech, 1985b

Species Overview:

Alexandrium tamarense is an armoured, marine, planktonic dinoflagellate. It is associated with toxic PSP blooms in cold water coastal regions.

Taxonomical Description:

Cells of A. tamarense are small to medium in size, almost isodiametric, and slightly longer than wide (Fig. 1). No apical horn is present. The first apical plate bears the ventral pore (Figs. 2,3). Cells are commonly found single or in pairs (Fig. 1), and less commonly in fours. Paired cells may contain an anterior attachment pore (aap) and a posterior attachment pore (pap) (Figs. 4,5). Thecal plates are smooth and thin (Figs. 1-3). The size and shape of this species is highly variable: cells range in size between 22-51 µm in length and 17-44 µm in transdiameter width (Lebour, 1925, Fukuyo et al., 1985, Fukuyo et al., 1990, Hallegraeff, 1991, Hallegraeff et al., 1991, Larsen and Moestrup, 1989, Balech, 1995, Taylor et al., 1995, Steidinger and 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. The apical pore plate (Po) houses a large fishhook shaped foramen and a small round aap (Figs. 2,4). The first apical plate (1') (Figs. 2,3) is variable in shape: from a broad triangle to a narrow rectangle, and bears a small ventral pore. The 1' plate comes in direct contact with the Po (Fig. 2) (Lebour, 1925, Fukuyo et al., 1985, Fukuyo et al., 1990, Larsen and Moestrup, 1989, Balech, 1995, Taylor et al., 1995, Steidinger and Tangen, 1996).

The epitheca and hypotheca are nearly equal in height (Figs. 1,6). The epitheca is broadly conical (Figs. 1,6), while the hypotheca is roughly trapezoidal (Figs. 1,6). The posterior end is slightly indented resulting in two hypothecal lobes; the left lobe is slightly larger than the right (Figs. 1,6). The deeply excavated cingulum is displaced in a descending fashion one time its width; it has a narrow list (Figs. 1,2,6). The deep sulcus, with lists, widens posteriorly (Fig. 1). The pap, if present, is small and located in the right half of the posterior sulcal plate (Fig. 5) (Lebour, 1925, Fukuyo et al., 1985, Fukuyo et al., 1990, Larsen and Moestrup, 1989, Balech, 1995, Taylor et al., 1995, Steidinger and 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 (Fukuyo, 1985, Larsen and Moestrup, 1989).


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 (Figs. 7,8) (Loeblich and Loeblich, 1975, Turpin et al., 1978, Silva, 1962).

Species Comparisons:

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 and Moestrup, 1989, Steidinger and Tangen, 1996).

A. tamarense is very similar morphologically (size, shape and thecal plate formula) to A. catenella ; both also produce deadly PSP toxins. Morphological differences lie in the shape of the Po, and presence or absence of a vp: the Po in A. catenella is slightly smaller than that in A. tamarense, and the vp is absent (Fukuyo, 1985). Molecular testing conducted on A. catenella from Japan and A. tamarense from Japan and the U.S.A. revealed a close genetic relationship between the two species, however they remain distinct (Adachi et al., 1995).

Morphologically, A. fundyense is nearly identical to A. tamarense except for the missing ventral pore on the 1' plate. A. minutum can also be misidentified as A. tamarense; however, A. tamarense is a smaller species, is always longer than wide, and is found in colder waters than A. minutum (Balech, 1995, Hallegraeff, 1991, Larsen and Moestrup, 1989, Steidinger and Tangen, 1996).


A. tamarense is a planktonic dinoflagellate species associated with toxic 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 and Hansen, 1988), and are common along the NE coast of North America (New England and Canada) (Bicknell and Walsh, 1975, Hurst, 1975, Loeblich and Loeblich, 1975). During a red tide event reported in the Faroe Islands, Norway, in 1984, population levels of A. tamarense were estimated at 1 X 10^7 cells/L and completely dominated the plankton (Mortensen, 1985, Moestrup and Hansen, 1988).

This species produces a ellipsoidal resting cyst that cannot be distinguished from the cyst produced by A. catenella. This cyst has rounded ends with a thick cell wall, and is covered in mucilage (Figs. 7,8). Cysts often contain colorless granules and distinct reddish lipid bodies. Size ranges from 36-56 µm in length and 23-32 µm in width (Turpin et al., 1978, Fukuyo, 1985, Bolch and Hallegraeff, 1990, Hallegraeff, 1991, Hallegraeff et al., 1991).


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 and Moestrup, 1989): GTX I, II, III, IV and V, neosaxitoxin and saxitoxin (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.

Not all strains of A. tamarense are toxic: both toxic and nontoxic strains have been reported in New England within the same red tide event (Yentsch et al., 1978). Strains in Australia (Hallegraeff, 1991), River Tamar estuary, Britain (type locality) (Moestrup and Hansen, 1988) and the Gulf of Thailand (Fukuyo et al., 1988) are all non-toxic.

The usual route of PSP toxin transmission is via tainted shellfish; however, bloom events of A. tamarense have been linked to several massive fish kills: Atlantic herring in the Bay of Fundy, Canada (White, 1980); and rainbow trout and salmon in the Faroe Islands, Norway (Mortensen, 1985). Hayashi et al., 1982 attribute the fish kills to dinoflagellate toxins accumulated in the food chain; i.e. fish feed on zooplankton infected with PSP poisons and die. However, Ogata and Kodama, 1986 report production of ichthyotoxins in cultured media of this species.

Habitat and Locality:

A. tamarense is a widely distributed coastal and estuarine dinoflagellate species (Lebour, 1925, Steidinger and 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 and Tangen, 1996, Taylor et al., 1995).

Alexandrium tamarense