Identifying Harmful Marine Dinoflagellates

Cochlodinium polykrikoides
Margelef, 1961
Plate 9, Figs. 1-7

Species Overview: Cochlodinium polykrikoides is an unarmoured, marine, planktonic dinoflagellate species with a distinctive spiral-shaped cingulum. It is a common red tide former associated with fish kills in Japan and Korea.

Taxonomic Description: Cochlodinium polykrikoides is an athecate species; i.e. without thecal plates. Cells are small, oval and slightly flattened dorso-ventrally (Figs. 1, 2). Chains, rarely more than eight cells, are common (Figs. 1-4). An apical groove is present on the apex originating from the anterior end of the cingular and sulcal juncture and extending to the dorsal side of the epitheca. Cells range in size from 30-40 um in length to 20-30 um in width (Silva 1967; Yuki & Yoshimatsu 1989; Fukuyo et al. 1990; Taylor et al. 1995; Steidinger & Tangen 1996).
The epitheca is conical and rounded at the apex (Figs. 1, 2, 4). The hypotheca is bilobed (Fig. 1). The cingulum is deep and excavated (Figs. 1, 2, 4). It is displaced about 0.6 times the cell length, and descends in a distinct left-handed spiral of 1.8-1.9 turns around the cell. The narrow and shallow sulcus nearly runs parallel to the cingulum making 0.8-0.9 turns around the cell between the proximal and distal ends of the cingulum. The sulcus deepens and widens towards the antapex and divides the hypotheca into two asymmetrical lobes (Fig. 1). The right lobe is narrower and slightly longer than the left lobe (Silva 1967; Yuki & Yoshimatsu 1989; Fukuyo et al. 1990; Taylor et al. 1995; Steidinger & Tangen 1996). Trichocysts have been observed in this species, but the number per cell varies, and not all cells bear them. The presence and number of trichocysts increases with cell and culture age (Silva 1967).

Nomenclatural Types:
Holotype: Cochlodinium polykrikoides Margelef, 1961: 76, fig. 27
Type Locality: Caribbean Sea: Puerto Rico
Synonyms: Cochlodinium heterolobatum Silva, 1967

Morphology and Structure: C. polykrikoides is a photosynthetic species with numerous yellowish-green to brown chloroplasts, rod-shaped or ellipsoid in shape (Fig. 1). The nucleus is situated anteriorly in the epitheca (Figs. 2, 4). A red stigma is present dorsally in the epitheca (Silva 1967; Yuki & Yoshimatsu 1989; Fukuyo et al. 1990; Taylor et al. 1995).

Reproduction: C. polykrikoides reproduces asexually by binary fission; plane of fission is oblique (Silva 1967).

Ecology: C. polykrikoides is a planktonic species. It is a common ichthyotoxic 'red water' bloom species in the northwestern Pacific. This species commonly forms cysts (Figs. 5-7) (Fukuyo et al. 1990; Taylor et al. 1995; Steidinger & Tangen 1996).

Toxicity: Cochlodinium polykrikoides is a known red tide species associated with extensive fish kills and great economic loss in Japanese and Korean waters (Yuki & Yoshimatsu 1989; Fukuyo et al. 1990; Kim 1998). However, the actual toxin principles have yet to be ellucidated (Taylor et al. 1995). Ho and Zubkoff (1979) suggested that physical contact, not a released toxin, was the cause of oyster larvae (Crassostrea virginica) deformation and mortality during a C. polykrikoides red tide in the York River (Virginia, USA).

Species Comparison: C. polykrikoides closely esembles two other Cochlodinium species: C. helix and C. helicoides. The degree of rotation of the cingulum and sulcus distinguish the former species from the latter two: a. the cingulum in C. polykrikoides makes 1.8-1.9 turns around the cell, while in C. helix it is two turns and in C. helicoides it is 1.5 turns; and b. the sulcus turns 0.8 times between the proximal and distal ends of the cingulum in C. polykrikoides, whereas it is 1 time in C. helix and 0.6 times in C. helicoides (Silva 1967).

Habitat and Locality: C. polykrikoides is a cosmo-politan species found in warm temperate and tropical waters (Steidinger & Tangen 1996). This species was first reported from the Caribbean Sea along the southern coast of Puerto Rico (Margelef 1961). It has since been reported in northern Atlantic waters along the American east coast: Barnegat Bay, New Jersey (Silva 1967), and the York River, Virginia (Ho & Zubkoff 1979; Zubkoff et al. 1979). It is widely distributed in northwestern Pacific waters along the coasts of Japan and Korea (Fukuyo et al. 1990; Kim 1998).

Figure 1: Morphology of a Dinoflagellate