Superoxide production rates and hemolytic activity linked to cellular growth phases in Chattonella species (Raphidophyceae) and Margalefidinium polykrikoides (Dinophyceae)

The increased occurrence of ichthyotoxic blooms of Chattonella and Margalefidinium species has led to mass fish kills causing multi-million dollar economic losses in diverse marine environments. Their ichthyotoxicity may be driven by a synergistic effect of diverse chemical compounds, of which little is understood in terms of production and biological activity. This study analyzed the growth rates, superoxide radical (O₂^●−) production rate, lipid peroxidation (TBARS) levels, and hemolytic activity of the ichthyotoxic raphidophytes Chattonella complex (C. var. marina, C. var. ovata, C. var. antiqua), C. subsalsa and the dinoflagellate Margalefidinium polykrikoides. Growth interactions between Chattonella and M. polykrikoides were also analyzed in bi-algal cultures. Chattonella strains exhibited higher growth rates than M. polykrikoides in monocultures. Highest O₂^●− production rate and TBARS levels in cells occurred in the early exponential growth phase, where M. polykrikoides showed higher values compared with Chattonella strains. Highest hemolytic activity associated to higher cell abundance was caused by M. polykrikoides followed by raphidophytes during the stationary and exponential growth phase, respectively. Of the three Chattonella strains, only C. subsalsa growth was inhibited when grown in bi-algal cultures with M. polykrikoides. In conclusion, this study supports an ecological linkage between cell growth conditions and a dynamic production of O₂^●− and/or hemolysins, which may mediate its ichthyotoxicity. However, the potential involvement in mass fish kills and ecological implications for local trophic webs remains to be further elucidated.