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Gyrodinium galatheanum (Braarud) Taylor, 1992

Species Overview:

Gyrodinium galatheanum is an unarmoured, marine, planktonic dinoflagellate species. It is a common red tide former discovered in Walvis Bay, South Africa, associated with fish kills.

Taxonomic Description:

Gyrodinium galatheanum is an athecate species; i.e. without thecal plates. Cells are small and oval to round in ventral view (Figs. 1-5). A well-defined apical groove is present ventrally on the anterior of the cell (Figs. 1,2,5). The apical groove can produce a slight indentation at the apex (Figs. 4,5). Cells range in size from 9-17 µm in length to 8-14 µm in width (Braarud, 1957, Taylor et al., 1995, Steidinger and Tangen, 1996).

The epitheca and hypotheca are both round (Figs. 1-5). The cingulum is displaced in a descending fashion up to 3 times its width (Figs. 1-5). The broad cingulum is deeply excavated and houses the transverse flagellum (Figs. 1,2,5). The narrow sulcus slightly invades the epitheca adjacent to the apical groove (Figs. 1,2,5) (Braarud, 1957, Taylor et al., 1995, Steidinger and Tangen, 1996).

Morphology and Structure:

G. galatheanum is a photosynthetic species with several rounded chloroplasts. The large nucleus is round and centrally located (Figs. 3,5). This species does not have peridinin as a major accessory pigment, but has a fucoxanthin derivative and chlorophyll c3 (Braarud, 1957, Bjornland and Tangen, 1979, Johnsen and Sakshaug, 1993, Taylor et al., 1995, Steidinger and Tangen, 1996).

Reproduction:

G. galatheanum reproduces asexually by binary fission.

Species Comparison:

In shape and size Gyrodinium galatheanum resembles two other small athecate gymnodinoids, G. veneficum and G. micrum (Taylor et al., 1995). Physiologically G. galatheanum is closely related to the toxic species Gyrodinium aureolum. Both lack peridinin while both have chlorophyll c3 , which is characteristic of several bloom-forming prymnesiophytes (Johnsen and Sakshaug, 1993).

Ecology:

G. galatheanum is a bloom-forming planktonic species. Blooms of this species were first recorded from Walvis Bay, South Africa (Braarud, 1957). Blooms have since been reported from the Oslofjord, Norway (Bjornland and Tangen, 1979) and along the southern coast of Norway (Dahl and Yndestad, 1985).

Li et al., 2000 recently observed mixotrophic behaviour in G. galatheanum from the Chesapeake Bay. This primarily photosynthetic species was observed feeding on cryptophytes under light and/or nutrient stressed conditions, suggesting that it may use phagotrophy to furnish major nutrients necessary for photosynthesis.

Toxicity:

G. galatheanum is a toxic species associated with fish kills in Walvis Bay, South Africa (Braarud, 1957, Steemann and Aabye Jensen, 1957, Pieterse and Van Der Post, 1967). Although this species has been linked to marine life mortalities, mussels and juvenile cod (Nielsen and Stromgren, 1991, Nielsen, 1993), the toxin principles have yet to be determined (Copenhagen, 1953, Pieterse and Van Der Post, 1967).

Habitat and Locality:

This species has been reported from cold waters in the North and South Atlantic Oceans: North Sea, British Isles (Larsen and Moestrup, 1989); Oslofjord, Norway (Bjornland and Tangen, 1979); and Walvis Bay, South Africa (Braarud, 1957). G. galatheanum may be a wide-spread species but due to its minute size, it most likely has been greatly overlooked in phytoplankton assessments (Taylor et al., 1995).

Gyrodinium galatheanum