Morphotaxonomy and genetic affinities of five novel, potentially fish-killing, Australian gymnodinioid dinoflagellates
Creators: name: de Salas, MF
Publisher: name: University Of Tasmania
Year: 2023

description: Water samples from several southern Australian locations (Tasmania, Victoria, New South Wales, South Australia and Western Australia) have revealed a range of previously undescribed gymnodinioid dinoflagellates. Five new species are described in this study, from field samples and laboratory cultures, with the use of light microscopy, scanning and transmission electron microscopy, pigment analysis and sequencing of the large subunit ribosomal gene (LSU rDNA). Karenia umbella de Salas, Bolch &amp; Hallegraeff sp. nov., has a straight apical groove typical of the genus. This species is morphologically similar to K. longicanalis but has an asymmetrically shaped hypocone, irregularly shaped chloroplasts, and is ornamented by 8 radial furrows on the epicone surface. Karenia asterichroma de Salas, Bolch &amp; Hallegraeff sp. nov. is a dorso-ventrally flattened unarmoured dinoflagellate resembling K. brevis. Unlike other known Karenia species, the chloroplasts of K asterichroma radiate from a central pyrenoid, and its nucleus is located in the centre of the epicone. While the ichthyotoxicity of K asterichroma is yet to be confirmed, it was associated, together with K. umbella and further undescribed Karenia species, with the recent mass mortality in May 2003 of over 100,000 salmonoids in an aquaculture facility in southern Tasmania. A new, potentially ichthyotoxic genus, Takayama de Salas, Bolch, Botes et Hallegraeff gen. nov. is described with two new species: T. tasmanica de Salas, Bolch et Hallegraeff, sp. nov., and T helix, de Salas, Bolch, Botes et Hallegraeff, sp. nov., isolated from Tasmanian (Australia) and South African coastal waters. The new Takayama species have sigmoid apical grooves and close affinities to the other fucoxanthin-containing genera Karenia and Karlodinium. A new mixotrophic species in the toxigenic genus Karlodinium, K. australe de Salas, Bolch &amp; Hallegraeff sp. nov., is morphologically similar to Gyrodinium corsicum and Karenia digitata but has an anteriorly located nucleus and a different amphiesmal pattern. K. australe lacks the hexagonal arrays of plug-like structures below the amphiesma that define the genus, and its chloroplasts contain pyramidal rather than lenticular pyrenoids. Thus the definition of Karlodinium needs to be emended, as it is too narrow, and currently excludes K australe. Pigment analyses of these species, all from previously well studied fish-killing groups, have determined that they contain fucoxanthin and its derivatives as the main accessory pigments. The pigment gyroxanthin-diester, was present in all Karenia species tested, but its presence was variable in Karlodinium and Takayama. Furthermore, phylogenetic analysis of these and other gymnodinioid species show that all the fucoxanthin-containing, fish-killing species in the genera Karenia, Karlodinium and Takayama form a well-defined, monophyletic clade within the Gymnodiniales. The description and detailed characterisation of these five new species will help design more effective monitoring tools, such as molecular probes, for the early detection of these potentially fish killing dinoflagellates.