Toxic effects of three closely-related dinoflagellates, Karenia concordia, K. brevisulcata and K. mikimotoi (Gymnodiniales, Dinophyceae) on other microalgal species

In this study the aggregate effects of lipophilic toxins extracted from cultures of three closely-related dinoflagellates, Karenia concordia, Karenia brevisulcata and Karenia mikimotoi, on 18 species of microalgae from five algal classes, have been evaluated. In terms of toxicity, cells of all 5 algal classes tested are found to be more vulnerable to those produced by K. brevisulcata and K. concordia than that of K. mikimotoi. Toxin extracts of both K. brevisulcata and K. concordia destroyed cells in a matter of few minutes to tens of minutes (‘fast-acting’) and that of K. mikimotoi in tens of minutes to hours (‘slow-acting’). Overall, cells of both the flagellates (Class Cryptophyceae, Class Raphidophyceae and Class Prasinophyceae) and diatoms (Class Bacillariophyceae) were more sensitive to toxin extracts of all the three Karenia spp. than those of dinoflagellates (both armoured and unarmoured) (Class Dinophyceae). Cells of both Chattonella marina and Alexandrium catenella, sensitive to toxin extracts of all three Karenia spp., were found to exhibit distinct responses before cell destruction. In the case of A. catenella, cells exposed to toxin extract of K. concordia showed partial disintegration of both the theca wall and the cytoplasmic membrane. These effects were not observed in cells exposed to those of K. brevisulcata and K. mikimotoi. The unique response of A. catenella cells to toxin extract of K. concordia is discussed.

Research highlights▶ The aggregate toxic effects of three harmful dinoflagellates, Karenia concordia, K. brevisulcata and K. mikimotoi were evaluated. ▶ Toxins produced by both Karenia concordia and K. brevisulcata have been found to act more quickly on the test organisms than those of K. mikimotoi. ▶ A new sensitive bioassay for K. concordia toxins has been developed.