Analysis of the Mutual Influence of the Microalgae Heterosigma akashiwo (Raphidophyceae) and Thalassiosira pseudonana (Bacillariophyta).

The mutual influence of the rafidophyte microalgae Heterosigma akashiwo, which causes algal blooms, and the diatom Thalassiosira pseudonana, which is regularly present in sea waters, was studied under experimental conditions. Experiments were carried out with monocultures, monocultural filtrates, and mixed cultures of different initial concentrations. The growth and physiological state of the microalgae were assessed by flow cytometry. Both algae displayed inhibited growth in co-culture and on filtrates, but growth was suppressed to a greater extent in T. pseudonana. The fluorescence of chlorophyll a and the contents of reactive oxygen species and neutral lipids decreased in H. akashiwo cultures grown on T. pseudonana filtrate. Similar changes were noted in a T. pseudonana culture grown on H. akashiwo filtrate. It is concluded that these algae exhibit allelopathic activity in relation to each other. [ABSTRACT FROM AUTHOR]