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Gymnodinium pulchellum Larsen, 1994

Species Overview:

Gymnodinium pulchellum is an unarmoured, marine, planktonic dinoflagellate species. This species produces red tide blooms and has been associated with fish and invertebrate kills in Japan and Florida.

Taxonomic Description:

Gymnodinium pulchellum is an athecate species; i.e. without thecal plates. Cells are small and broadly oval with slight dorso-ventral compression (Figs. 1-6). The ventral surface is flattened; the dorsal surface is rounded. A conspicuous and well-defined sigmoid apical groove is present on the epitheca (Fig. 1); the groove is a characteristic reversed S-shape (Fig. 2). Cells range in size from 16-25 µm in length to 11-16 µm in width (Fukuyo et al., 1990, Larsen, 1994, Taylor et al., 1995, Steidinger and Tangen, 1996, Steidinger et al., 1998).

The epitheca is slightly smaller than the hypotheca. The wide and deeply excavated cingulum is premedian, and is displaced in a descending fashion 1-1.5 times its width (Figs. 1,3,4). The sulcus invades the epitheca slightly as a finger-like projection (Fig. 2). The sulcus widens and deepens towards the posterior of the cell creating a bilobed hypotheca (Figs. 1,3,4) (Larsen, 1994, Taylor et al., 1995, Steidinger and Tangen, 1996, Steidinger et al., 1998).

Morphology and Structure:

G. pulchellum is a photosynthetic species with several yellowish-brown chloroplasts. Pyrenoids are also present (Figs. 3,4). The large nucleus is ellipsoidal and located in the left part of the cell (Figs. 5,6) (Fukuyo et al., 1990, Larsen, 1994, Steidinger and Tangen, 1996, Steidinger et al., 1998).

Reproduction:

G. pulchellum reproduces asexually by binary fission.

Species Comparisons:

Sharing the same habitat and locale, and the same general shape, G. pulchellum can be confused with G. mikimotoi. G. pulchellum, however, is smaller in size and has a distinctive sigmoid apical groove; the apical groove of G. mikimotoi is straight (Larsen, 1994).

Ecology:

G. pulchellum is a planktonic species first described from southeastern Australia. This species is a bloom-former associated with extensive fish and invertebrate kills in southeast Florida. During one red tide event waters turned an orange-red color with cell levels recorded as high as 19.7 X 10^6 cells/L (Steidinger et al., 1998).

Toxicity:

G. pulchellum is a toxic species associated with fish and invertebrate kills from southeast Florida. The presence of this species at two separate fish kills in the Indian River, FL, suggests it is ichthyotoxic (Steidinger et al., 1998). Onoue et al., 1985 demonstrated that G. pulchellum (as Gymnodinium type '84-K) is ichthyotoxic. Three toxic fractions have been isolated from this species: neurotoxic, hemolytic and hemaglutinative (Onoue and Nozawa, 1989). G. pulchellum is most likely responsible for fish kills in the Melbourne, Australia, region (Larsen, 1994).

Habitat and Locality:

This species is found in temperate to tropical neritic waters. It has been reported from Hobsons Bay (Melbourne area), Australia, where it is often common during the austral summer and early autumn (Larsen, 1994). It has also been recorded from Tasmanian waters (Hallegraeff, 1991), Japanese waters (Fukuyo et al., 1990; Onoue et al., 1985; Takayama, 1985) and from the Mediterranean (Carrada et al., 1991). More recently it has been identified in the western Atlantic off the east coast of Florida (Steidinger et al., 1998). Due to its minute size, G. pulchellum may have been greatly overlooked in phytoplankton assessments (Taylor et al., 1995).

Gymnodinium pulchellum