Le microflagelle Phaeocystis et la production heterotrophe bacterienne marine

Phaeocystis , a nanoplanktonic algae, appears in the eastern Channel and in the south of the North Sea, at the end of the microplanktonic spring outburst, with often considerable density. At that time, acrylic acid is excreted in the water. On account of its well known antibiotic activity, one could wonder if a bloom of Phaeocystis might be responsible for an antibacterial effect of the sea water. Acrylic acid has been detected in spring 1981 during the Phaeocystis bloom. Its concentration was greatly inferior to the 50% inhibitory concentration measured in vitro against natural bacterial population. Furthermore, results about primary and heterotrophic productions show a sharp synchronism in the peak of intensity. This means, at least, there is no inhibition of the heterotrophic activity by excreted acrylic acid. These results are discussed in conclusion.