Karenia asterichroma sp. nov. (Gymnodiniales, Dinophyceae), a new dinoflagellate species associated with finfish aquaculture mortalities in Tasmania, Australia

A new species of unarmoured dinoflagellate is described from Tasmanian field samples and laboratory cultures: Karenia asterichroma de Salas, Bolch & Hallegraeff, sp. nov. This species is characterized by the use of light and scanning electron microscopy and sequencing of the 26S ribosomal RNA gene. Karenia asterichroma is a dorsoventrally flattened cell resembling K. brevis, although it differs from this species by 4.5% in the D1-D3 regions of its 26S ribosomal DNA (rDNA) sequence. Unlike other Karenia species, the epicone of K. asterichroma has concave sides and the chloroplasts radiate from a central, putative pyrenoid. The nucleus is located in the centre of the epicone and the apical groove is long, extending ventrally to near a broad sulcal extension into the epicone. Partial 26S rDNA sequences indicate a relationship with K. bicuneiformis. Although the ichthyotoxicity of K. asterichroma is yet to be confirmed, it was associated (with three other Karenia species) with a recent mass mortality of over 100,000 caged salmonids at an aquaculture operation in southern Tasmania, Australia.