Karenia digitata sp nov (Gymnodiniales, Dinophyceae), a new harmful algal bloom species from the coastal waters of west Japan and Hong Kong

A new unarmoured dinoflagellate, Karenia digitata Yang, Takayama, Matsuoka & Hod,kiss sp. nov., is described on the basis of light and electron microscopy. It has bloomed in Hong Kong and Japan, and has caused significant fish kills and financial loss. High ichthyotoxicity persisted for approximately one week after the blooms had subsided. Karenia digitata cells are 10-26.25 mum long and 10-22.5 mum wide. The epicone is hemispherical or broadly conical; the hypocone is hemispherical and is not concave at the antapex. The girdle displacement varies but is more than 20% of the body length. The sulcus continues into the epicone as small finger-like extensions; it does not reach the antapex. At its centre it is displaced by the girdle. Chloroplasts are numerous, irregular in shape and randomly distributed, though usually clumped. The nucleus is spherical to ovoid and centrally to posteriorly located. The cell has an apical groove, which lies to the right of the sulcal axis, extends in a straight line over the apex to about one-third to half-way down the dorsal epicone, and gradually narrows near its centre. Karenia digitata may be confused with Gymnodinium pulchellum based on size, but the latter has a sigmoid apical groove. Kale,zia digitata shares features with Gyrodinium aureolum, Gymnodinium mikimotoi and Gymnodinium brevisulcatum [recently transferred to the genera Gymnodinium, Karenia and Karenia, respectively, by Daugbjerg et nl. (2000) (Phycologia 39: 302-317)], but differs from them in aspects such as overall appearance, cell thickness, size, the apical groove, sulcus arrangement and the shape and location of the nucleus. It closely resembles Gymnodinium vitiligo and Gymnodinium veneficum (both now transferred to the genus Karlodinium), except that these species are smaller and have a sulcus that extends onto the epicone.