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).
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 (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).