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Alexandrium catenella (Whedon and Kofoid) Balech, 1985b

Species Overview:

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

Taxonomical Description:

A chain-forming species, A. catenella typically occurs in characteristic short chains of 2, 4 or 8 cells (Figs. 1,5). Single cells are round, slightly wider than long, and are anterio-posteriorly compressed (Figs. 1,5,8). A small to medium sized species, it has a rounded apex and a slightly concave antapex (Figs. 1,5,8). The thecal plates are thin and sparsely porulated. Cells range in size between 20-48 µm in length and 18-32 µm in width (Fukuyo, 1985, Fukuyo et al., 1985, Fukuyo et al., 1990, Hallegraeff, 1991, Taylor et al., 1995, Steidinger and Tangen, 1996).

Thecal Plate Description:

The plate formula for A. catenella is: Po, 4', 6'', 6c, 8s, 5''', 2''''. The epitheca and hypotheca are nearly equal in height. The hypotheca bears prominent sulcal lists that resemble spines (Fig. 1). In chain forms, anterior attachment pores (aap) and posterior attachment pores (pap) are present (Fig. 2) (Fukuyo, 1985, Fukuyo et al., 1985, Fukuyo et al., 1990, Hallegraeff, 1991, Taylor et al., 1995, Steidinger and Tangen, 1996).

The apical pore complex (APC) is broad, triangular and widens dorsally (Figs. 2,3,9). The apical pore plate (Po) houses the characteristic fishhook shaped foramen, and, if catenate, an ellipsoidal anterior attachment pore (aap) (Figs. 2,9). There are two diagnostic features of this species: a.) the first apical plate, 1', comes in contact with the Po; and b.) a ventral pore (vp) is absent (Figs. 2-4,9). The median cingulum is lipped, deeply concave, and is displaced in a descending fashion one time its width (Figs. 1,8). The sulcus is deeply impressed and widens posteriorly (Figs. 1,8). The wide posterior sulcal plate houses the pap near the right margin (Fukuyo, 1985, Fukuyo et al., 1985, Fukuyo et al., 1990, Hallegraeff, 1991, Taylor et al., 1995, Steidinger and Tangen, 1996).

Morphology and Structure:

A. catenella is a photosynthetic species with numerous yellow-green to orange-brown chloroplasts. The nucleus is large and U-shaped (Whedon and Kofoid, 1936).

Reproduction:

A. catenella reproduces asexually by binary fission. This species also has a sexual cycle with opposite mating types (heterothallism). After gamete fusion, a planozygote forms which then encysts into a characteristic resting cyst (Figs. 6,7) (Yoshimatsu, 1981).

Species Comparisons:

A. catenella is very similar morphologically (size, shape and thecal plate formula) to A. tamarense. Differences lie in the shape of the Po, and presence or absence of a vp. The Po in the former species is slightly smaller, and the vp is absent (Figs. 2,3) (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).
Chains of this species are quite distinctive, but can resemble A. tamiyavanichi; however, A. tamiyavanichi is a warm water species and can be distinguished from A. catenella by its conical shape (Taylor et al., 1995).

Ecology:

A. catenella is a planktonic dinoflagellate species associated with deadly PSP events mostly in the Pacific Ocean. Red tides of this species have also been observed (Fukuyo, 1985).

This species produces a colorless resting cyst as part of its life cycle which cannot be distinguished from the cyst produced by A. tamarense (Figs. 6,7). The cyst is roughly ellipsoidal with rounded ends; it is covered by a smooth wall and a mucilaginous substance. Cysts have a wide size range: 38-56 µm in length to 23-32 µm in width (Fukuyo, 1985, Hallegraeff, 1991, Meksumpun et al., 1994).

Toxicity:

Alexandrium catenella is a known toxin-producing dinoflagellate species; it is the first species ever linked to paralytic shellfish poisoning, PSP. A. catenella produces strong PSP toxins which are transmitted via tainted shellfish: c1-c4 toxins, saxitoxins and gonyautoxins (Fukuyo, 1985, Fukuyo et al., 1985, Fukuyo et al., 1990, Hallegraeff, 1991, Taylor et al., 1995). These toxins can affect humans, other mammals, fish and birds (Prakash et al., 1971). Moreover, Ogata and Kodama, 1986 report production of ichthyotoxins in cultured media of A. catenella.

This species is responsible for numerous human illnesses and several deaths after consumption of tainted shellfish. Toxic blooms and PSP in shellfish have been reported in Chile (Avaria, 1979), Japan (Onoue et al., 1980, Onoue et al., 1981a, Onoue et al., 1981b), California (Sharpe, 1981) and most of the Pacific coast of the U.S.A. (Nishitani and Chew, 1988).

Habitat and Locality:

Alexandrium catenella is widely distributed in cold temperate coastal waters. Populations have been recorded from the west coast of North America (from California to Alaska), Chile, Argentina, western South Africa, Japan, Australia and Tasmania (Fukuyo, 1985, Fukuyo et al., 1985, Fukuyo et al., 1990, Hallegraeff, 1991, Hallegraeff et al., 1991, Taylor et al., 1995, Steidinger and Tangen, 1996).

Alexandrium catenella