Alexandrium catenella
(Whedon et Kofoid) Balech, 1985
Plate 2, Figs. 1-6

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

Taxonomic Description: A chain-forming species species, A. catenella typically occurs in characteristic short chains of 2, 4 or 8 cells (Figs. 1,2). Single cells are round, slightly wider than long, and are anterio-posteriorly compressed. A small to medium sized species, it has a rounded apex and a slightly concave antapex (Fig. 1). The thecal plates are thin (Fig. 3) and sparsely porulated. Cells range in size between 20-48 µm in length and 18-32 µm in width (Fukuyo 1985; Fukuyo et al. 1990; Hallegraeff 1991; Taylor et al. 1995; Steidinger & Tangen 1996).

Nomenclatural Types:
Holotype: Gonyaulax catenella Whedon and Kofoid, 1936: 25-31, figs. 1-7, 14, 15
Type Locality: NW Pacific Ocean: San Diego, California, USA
Synonyms: Gonyaulax catenella Whedon and Kofoid, 1936
Protogonyaulax catenella (Whedon and Kofoid) Taylor, 1979

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. 4) (Fukuyo 1985; Fukuyo et al. 1990; Hallegraeff 1991; Taylor et al. 1995; Steidinger & Tangen 1996).
The apical pore complex (APC) is broad, triangular and widens dorsally (Figs. 3, 4). The apical pore plate (Po) houses the characteristic fishhook shaped foramen, and, if catenate, an ellipsoidal aap (Fig. 4). There are two diagnostic features of this species: a.) the first apical plate, 1', comes in contact with the Po (Fig. 3); and b.) a ventral pore (vp) is absent. The median cingulum is lipped, deeply concave, and is displaced in a descending fashion one time its width (Figs. 1, 5). The sulcus, with prominent lists, is deeply impressed and widens posteriorly (Figs. 1, 5). The wide posterior sulcal plate houses the pap near the right margin (Fukuyo 1985; Fukuyo et al. 1990; Hallegraeff 1991; Taylor et al. 1995; Steidinger & 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 & 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 (Fig. 6) (Yoshimatsu 1981).

Ecology: A. catenella is a planktonic dinoflagellate species associated with deadly paralytic shellfish poisoning (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 (Fig. 6). 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 PSP (Fukuyo 1985; Fukuyo et al. 1990; Hallegraeff 1991; Taylor et al. 1995). A. catenella produces strong PSP toxins which are transmitted via tainted shellfish. These toxins can affect humans, other mammals, fish and birds: c1-c4 toxins, saxitoxins (SXT) and gonyautoxins (GTX)(Schantz et al. 1966; 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 infected shellfish. Toxic blooms and PSP in shellfish have been reported in Chile (Avaria 1979), Japan (Onoue et al. 1980; 1981a; 1981b), California (Sharpe 1981) and most of the Pacific coast of the U.S.A. (Nishitani & Chew 1988).

Species Comparison: 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 (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).

Habitat and Locality: A. 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. 1990; Hallegraeff 1991; Hallegraeff et al. 1991; Taylor et al. 1995; Steidinger & Tangen 1996).

Figure 1: Morphology of a Dinoflagellate

Glossary

Bibliography