Gymnodinium aureolum

This species is not toxic, but is morphologically very similar to species that are.

This species has been found in Irish waters. Visible mortalities included sea urchins, lugworms and several wild fish species were also found dead. The mortalities have been suggested to have been caused by a combination of low oxygen levels and the presence of toxins. The production of high rates of viscous extracellular polysaccharides can cause asphyxiation in fish, a property called ?rheotoxicity"(Vanhoutte-Brunier et al. 2008).

Cells ovoid or ellipsoidal, slightly longer than wide. Cingulum usually median and relatively wide. Slightly dorso-ventrally flattened. Sulcus extends from the antapex and about three quarters of the way onto the epicone. Cell contains many irregular, branching plastids, not laid out in any particular pattern (Hansen et al. 2000).

There has been confusion over the taxonomy of this species and Karenia mikimotoi in the past. Even though it appears to be resolved now, one must check literature carefully, to ensure they are not getting information on the wrong species. The European clade of G. aureolum does appear to be the same species as in North America, and not synonamous with K. mikimotoi (Hansen et al. 2000).

Usually found in temperate and sub-arctic waters during unusually warm periods for the particular location, especially in the northern hemisphere.

Gymnodinium aureolum is an unarmoured dinoflagellate that uses light from the sun to photosynthesize. It is not a HAB species.

Temperature- 12.5-22.5°C; Salinity- 17.8-34 PSU

Use longitudinal flagellum for direction, and for forward motion use the transverse flagellum, following a pronounced helical path (Ekelund & Häder 1988).

This species is easily confused with others in the complex but can be differentiated by the apical groove-sulcus juncture and ventral ridge (Tomas 1997).

Temperature: 15-27 ºC; Salinity approximately 35 PSU

Distribution: Temperate to tropical neritic waters; cosmopolitan

Migrates vertically in mixed water columns, but in stratified water the population remains confined to the pycnocline layer (Gentien et al. 2007).

The sulcus slightly invades the epitheca; immediately right is the proximal end of the apical groove which extends into the dorsal epitheca. Karenia mikimotoi cell shape is predominantly oval and is dorso-ventrally compressed. The cingulum is slightly displaced being twice the cingular width. The ventral ridge is inverted and hook shaped. Chloroplasts are present. The nucleus is ellipsoidal and on the left side near the periphery.

Karenia mikimotoi is one of the most common HAB causing species of dinoflagellate in the North Atlantic region and it is also commonly found around Japan. Blooms of this species are often considerable, reaching over a million cells per litre, and are associated with large marine fauna mortalities. The exact cause of the harmful effect is not yet fully understood, but measurements of cytotoxic polyethers have been extracted from cultures of this species (Silke et al. 2005).