Gymnodinium mikioto Miyake et Kominami ex Oda 1935
Gymnodinium breve Davis 1948
Morphological Characteristics :
Round to oval is shape. Flattened dorsal and ventral sides. Nucleus is often located in the left bottom lobe of the cell. Numerous rod-shaped or round chloroplasts. The girdle groove is wide and deeply incised, with a left-hand displacement about 2 times the girdle width. The sulcal groove widens out towards the lower cell half thus causing an invagination. A characteristic apical groove is present to the right of the sulcal axis in ventral view and extends in a straight line to the upper third of the dorsal upper cell half.
Hallegraeff (1991) stated that this dinoflagellate is closely related, perhaps identical, to Gymnodinium mikioto found in Australia and New Zealand. It was also said that the organism has a lot of similarities with Gymnodinium breve (Davis, 1948) sampled from the Gulf of Mexico, which is butterfly-shaped and has a prominent apical ridge.
Hallegraeff also claimed that this organism is identical to Gymnodinium nagasakiense. However, the G. nagasakiense found in Hong Kong waters is larger in size and has rather distinct lobes.
Size of Specimen :
15-32 mm (L), 10-28 mm (W)
Distribution :
The organism was reported to cause algal blooms and red tide in Florida, USA (1998), Gulf of Mexico (1948), North Island of New Zealand (1998) and sometimes in Australia. Also commonly be seen in Norway, Ireland and Scotland. Not very often been found in the South China Sea. However, the organism caused significant red tide in the spring of 1998. The red tide extended from Dapeng Bay, southern waters of Hong Kong to the Pearl River Estuary. It resulted with massive fishkill (>400 tonnes) with economic loss more than 250 million HK dollars.
Major Limiting Factors :
Dissolved inorganic nitrogen (DIN) and warm water temperature (18-23°C)
Toxicity :
Related to NSP in Australia. Caused human respiratory disorder (aerosol poisoning) in New Zealand(1998) and some areas of Australia.
