Molecular phylogeny and toxicity of harmful benthic dinoflagellates Coolia (Ostreopsidaceae, Dinophyceae) in a sub-tropical marine ecosystem: The first record from Hong Kong

Coolia are marine benthic dinoflagellates which are globally distributed and potentially toxic. This study provides the first investigation of species diversity and toxicity assessment of Coolia in Hong Kong waters. Fifty-one strains of four Coolia species, including C. malayensis, C. canariensis, C. tropicalis, and C. palmyrensis, were isolated from twelve sub-tidal habitats, and identified phylogenetically using 28S rDNA sequences. Exposure experiments (48-hour) demonstrated that the algal lysates extracted from the four Coolia species exhibited different toxic effects on the lethality and abnormality of two invertebrate larvae, i.e., brine shrimp Artemia franciscana and sea urchin Heliocidaris crassispina. Heliocidaris crassispina was more sensitive to the toxic effects of Coolia species than A. franciscana. Toxicity tests from both larvae revealed that C. malayensis was generally more toxic, and caused higher mortality rates when compared with the other three species. The emerging threat of harmful benthic dinoflagellates to marine environments and sensitive biota is discussed.