Gymnodinium catenatum

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 1 X 106 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; 1989), Venezuela (La Barbera-Sanchez et al. 1993), the Philippines (Fukuyo et al. 1993) and Europe (Estrada et al. 1984; Franca & Almeida 1989; Giacobbe et al. 1995).
G. catenatum produces a characteristic resting cyst (Fig. 6). Cysts are 42-52 µm in diameter, spherical and brown. They have a very distinct morphology: the surface is covered with microreticulate ornament t-tations. 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 & Bolch 1991).

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

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

Holotype: Gymnodinium catenatum Graham, 1943: 259-262, figs. 1, 2
Type Locality: NE Pacific Ocean: Gulf of California, Mexico

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 (Fig. 6). Nutrient deficiency induces the sexual phase (Blackburn et al. 1989).

G. catenatum can readily be distinguished from other Gymnodinium species by forming long chains, 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 & Moestrup 1989; Hallegraeff 1991; Taylor et al. 1995). Gyrodinium impudicum, recently described from Spain, can superficially resemble Gymnodinium catenatum with its similar horseshoe 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).

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.

Gymnodinium catenatum is an athecate species; i.e. without thecal plates. This species is typically seen in chain formation with up to 64 cells. Cells are small with morphology varying between single cell (Fig. 1) and chain formation (Figs. 2-4). Single cells are generally elongate-ovoid with slight dorso-ventral compression (Figs. 1, 5). The apex is truncate or slightly conical while the antapex is rounded and notched (Figs. 1, 5). Chain formers, in general, are squarish-ovoid with anterior-posterior compression (Fig. 3). A characteristic horseshoe shaped apical groove encircles the apex (Fig. 1) (Graham 1943; Larsen & Moestrup 1989; Fukuyo et al. 1990; Hallegraeff 1991; Taylor et al. 1995; Steidinger & 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. 2,3), similar to single cells (Graham 1943; Blackburn et al. 1989; Larsen & Moestrup 1989; Fukuyo et al. 1990; Hallegraeff 1991; Taylor et al. 1995; Steidinger & Tangen 1996).
The epitheca is smaller than the hypotheca, rounded or truncate (Figs. 1, 2). In chain-formers, the epitheca is conical (Figs. 2, 4). The larger hypotheca tapers slightly posteriorly (Figs. 2, 3). It is notched by the sulcus at the antapex creating a bilobed posterior (Fig. 5). The premedian cingulum displays left-handed displacement, about 2 times its width (Figs. 1, 2). The transverse flagellum is housed in the deep cingulum (Figs. 1-3). The sulcus is deep and extends almost the full length of the cell: from just beneath the apex to the antapex (Figs. 1-3) (Graham 1943; Larsen & Moestrup 1989; Fukuyo et al. 1990; Hallegraeff 1991; Taylor et al. 1995; Steidinger & Tangen 1996).

G. catenatum is a known paralytic shellfish poison (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).