Gymnodinium brevisulcatum sp nov (Gymnodiniales, Dinophyceae), a new species isolated from the 1998 summer toxic bloom in Wellington Harbour, New Zealand

Morphological characters of Gymnodinium brevisulcatum EH. Chang sp. nov. ar e described from specimens collected during the 1998 summer toxic bloom in Wellington Harbour and cultures developed from the bloom. The new species, which dominated the early 1998 bloom, is very toxic and killed a large vari ety of micro- and macroalgae, invertebrates, and vertebrates in the harbor. Human respiratory distress was experienced from aerosols apparently origin ating from the bloom. Isolates of G. brevisulcatum were examined using both light and scanning electron microscopy. Gymnodinium brevisulcatum may be s eparated from G. mikimotoi Miyake et Kominami ex Oda (= G. nagasakiense) an d other closely related species by several features: it has a very short ap ical groove on the ventral surface of the epicone; it is the smallest speci es within the Gymnodinium mikimotoi group; and the nucleus is either spheri cal and located in the left lobe of hypocone or at the division stage, it i s horizontally elongated, extending left to right in the hypocone.