Abstract

Heterosigma akashiwo is a bloom-forming planktonic flagellate that causes fish mortalities, which damages the aquaculture industry worldwide. In Chile, this species was reported for the first time in 1988 when it caused one of the most dramatic harmful algal blooms in the south of the country. At that time, an unialgal culture was set and used for a morphological characterization but, unfortunately, it was not maintained. In April 2013 a new outbreak of H. akashiwo was detected in the Maullin Estuary (41 degrees 37 ' S, 73 degrees 36 ' W), Southern Chile, causing fish mortalities in commercial salmon farms. An unialgal culture of this new Chilean population of H. akashiwo was obtained and has been maintained in the Culture Collection of Microalgae of the University of Concepcion, Chile, under the code CCM-UdeC 225. The aim of this study was to compare the morphological and physiological attributes of this Chilean strain of H. akashiwo with those of strains from France, Spain and New Zealand, in order to identify eventual intraspecific variability among them. Cell size, growth parameters, pigments profiles, photosynthetic attributes and toxicity were determined for the strains, grown under identical culture conditions. The Chilean strain exhibited the highest growth and accumulated the highest proportion of the carotenoid fucoxanthin, while strains from Chile and Spain were the less light-tolerant and had similar toxicity. These results reinforce previous findings about the high level of intraspecific variability within H. akashiwo including, for the first time, a strain from South America.