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Gymnodinium catenatum Graham, 1943

Species Overview:

Gymnodinium catenatum is an unarmoured, marine, planktonic dinoflagellate species. It is a chain-forming, toxin-producing, red tide species associated with PSP events throughout the world.

Taxonomic Description:

Gymnodinium catenatum is an athecate species; i.e. without thecal plates. This species is typically seen in chain formation (Figs. 4-9) with up to 64 cells. Cells are small with morphology varying between single cell and chain formation. Single cells are generally elongate-ovoid with slight dorso-ventral compression (Figs. 1-3). The apex is truncate or slightly conical while the antapex is rounded and notched (Figs. 1-3). Chain formers, in general, are squarish-ovoid with anterior-posterior compression (Figs. 4-7). A characteristic horse-shoe shaped apical groove encircles the apex (Fig. 1) (Graham, 1943, Larsen and Moestrup, 1989, Fukuyo et al., 1990, Hallegraeff, 1991, Taylor et al., 1995, Steidinger and Tangen, 1996).

Single cells range in size from 27-43 µm in width to 34-65 µm in length. Chain-forming cells are slightly smaller with sizes ranging from 27-43 µm in width to 23-60 µm in length; terminal cells are slightly larger (Figs. 4-8), similar to single cells (Graham, 1943, Blackburn et al., 1989, Larsen and Moestrup, 1989, Fukuyo et al., 1990, Hallegraeff, 1991, Taylor et al., 1995, Steidinger and Tangen, 1996).

The epitheca is smaller than the hypotheca, rounded or truncate (Figs. 1-3,9). In chain-formers, the epitheca is conical (Figs. 3-6). The larger hypotheca tapers slightly posteriorly. It is notched by the sulcus at the antapex creating a bilobed posterior (Figs. 1,3,5,8). The premedian cingulum is displaced about 2 times its width (Figs. 1,2). The transverse flagellum is housed in the deep cingulum (Figs. 1,4,9). The sulcus is deep and extends almost the full length of the cell: from just beneath the apex to the antapex (Figs. 1,4-6) (Graham, 1943, Larsen and Moestrup, 1989, Fukuyo et al., 1990, Hallegraeff, 1991, Taylor et al., 1995, Steidinger and Tangen, 1996).

Morphology and Structure:

Gymnodinium catenatum is a photosynthetic species with numerous yellow-brown chloroplasts and conspicuous pyrenoids. The large nucleus is centrally located. Lipid globules are also common (Fig. 2) (Graham, 1943, Larsen and Moestrup, 1989, Fukuyo et al., 1990, Hallegraeff, 1991, Taylor et al., 1995, Steidinger and Tangen, 1996).

Reproduction:

G. catenatum reproduces asexually by binary fission. This species also has a sexual cycle with opposite mating types (heterothallism). After gamete fusion, a planozygote forms, and after two weeks, this form encysts into a characteristic resting cyst (Figs. 10,11). Nutrient deficiency induces the sexual phase (Blackburn et al., 1989).

Species Comparison:

Gymnodinium catenatum can readily be distinguished from other Gymnodinium species by its long chain-formations, however, single cells can easily be misidentified. Chains of G. catenatum can resemble Alexandrium catenella, an anterio-posteriorly compressed species that forms short-chains, however, this species is a cold-water species and is armoured. Chains of G. catenatum can also be confused with Peridiniella catenata, another armoured chain-forming species. The latter species, however, is not toxic, is a cold-water species and has posterior spines (Larsen and Moestrup, 1989, Hallegraeff, 1991, Taylor et al., 1995).

Gyrodinium impudicum, recently described from Spain, can superficially resemble Gymnodinium catenatum with its similar horse-shoe shaped apical groove and its tendency toward chain formation. However, Gyrodinium impudicum is smaller in size, differs in shape, forms shorter chains and is not associated with PSP (Fraga et al., 1995).

Ecology:

G. catenatum is a planktonic red tide species. The first G. catenatum red tide was reported from the Gulf of California with populations close to 1X10^6 cells/L (Graham, 1943). Populations of this species have been recorded from Mexico (Mee et al., 1986), Japan (Ikeda et al., 1989), Australia (Hallegraeff et al., 1988, Hallegraeff et al., 1989), Venezuela (La Barbera-Sanchez, 1993), the Philippines (Fukuyo et al., 1993) and Europe (Estrada et al., 1984, Franca and Almeida, 1989, Giacobbe et al., 1995).

G. catenatum produces a characteristic resting cyst (Figs. 10,11). Cysts are 42-52 µm in diameter, spherical and brown. They have a very distinct morphology: the surface is covered with microreticulate ornamentations (Figs. 10,11). These cysts can germinate after just two weeks of dormancy and initiate new populations (Blackburn et al., 1989). Cysts are not only a reseeding tool, but also a disbursement agent: G. catenatum was introduced to Australian waters via ships' ballast water (Hallegraeff and Bolch, 1991).

Toxicity:

G. catenatum is a known PSP toxin producer (Morey-Gaines, 1982, Mee et al., 1986). This species is the only unarmoured dinoflagellate known to produce PSP toxins (Taylor et al., 1995). First reports of PSP associated with G. catenatum blooms were recorded in Spain (Estrada et al., 1984).

Habitat and Locality:

G. catenatum populations are found in warm, temperate coastal waters. Blooms have been reported in Mexico, Argentina, Europe, Australia and Japan (Hallegraeff, 1991).

Gymnodinium catenatum