Species resolution and global distribution of microreticulate dinoflagellate cysts

The distribution, abundance and morphology of microreticulate dinoflagellate cysts were examined from samples collected from the coastal waters of Australia, the Baltic Sea, Italy, Hong Kong and Uruguay. On the basis of a combination of size range, variation in microreticulate pattern, and cyst wall colour, the three microreticulate species Gymnodinium catenatum (36-62 μm diameter), Gymnodinium nolleri (25-40 μm) and Gymnodinium microreticulatum (17-29 μm) could be distinguished. Only G. catenatum and G. microreticulatum were found at Australian sites. Gymnodinium microreticulatum was rare but widespread in sediments from Tasmania and temperate and tropical sites on mainland Australia, whereas G. catenatum was restricted to the eastern coast of Tasmania, southern Victoria, Port Lincoln [South Australia (SA)] and the Hawkesbury Estuary [New South Wales (NSW)]. Significant variation in G. catenatum mean cyst size was observed between sites, with mean diameters varying from 40.1 μm (Hawkesbury River, NSW) to 52.3 μm (Port Lincoln, SA). Laboratory experiments suggest that cyst size may be predominantly a genetically determined, population-specific character, rather than being influenced by environmental parameters. Using the species criteria refined from the dataset, existing reports of microreticulate cysts are re-examined, and the global distribution of microreticulate cyst species and the biogeography of the toxic dinoflagellate G. catenatum are re-evaluated.