Species resolution and global distribution of microreticulate dinoflagellate cysts

The distribution, abundance and morphology of microreticulatedinoflagellate cysts were examined from samples collected fromthe coastal waters of Australia, the Baltic Sea, Italy, HongKong 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 (36–62µm diameter), Gymnodinium nolleri (25–40 µm)and Gymnodinium microreticulatum (17–29 µm) couldbe distinguished. Only G. catenatum and G. microreticulatumwere found at Australian sites. Gymnodinium microreticulatumwas rare but widespread in sediments from Tasmania and temperateand tropical sites on mainland Australia, whereas G. catenatumwas restricted to the eastern coast of Tasmania, southern Victoria,Port Lincoln South Australia (SA)] and the Hawkesbury EstuaryNew South Wales (NSW)]. Significant variation in G. catenatummean cyst size was observed between sites, with mean diametersvarying from 40.1 µm (Hawkesbury River, NSW) to 52.3 µm(Port Lincoln, SA). Laboratory experiments suggest that cystsize may be predominantly a genetically determined, population-specificcharacter, rather than being influenced by environmental parameters.Using the species criteria refined from the dataset, existingreports of microreticulate cysts are re-examined, and the globaldistribution of microreticulate cyst species and the biogeographyof the toxic dinoflagellate G. catenatum are re-evaluated.