High prevalence of infection by endophytic brown algae in populations of Laminaria spp. (Phaeophyceae)

The occurrence of microscopic algae that are endophytes and potential pathogens of kelps was quantified during 1994 in wild populations of Laminaria saccharina, L. hyperborea and L. digitata at Helgoland, North Sea. Microscopic examination of, in total, 1224 thalli showed that the prevalence of infection by endophytic algae was 85%, much higher than was inferred by gross lesions alone. Prevalence was high throughout the year with a minimum in spring. At a more exposed site, prevalence was higher and disease symptoms stronger than at a sheltered locality. Disease symptoms were more severe in shallower than in deeper water. Endophytes were not strictly host-specific, but L. saccharina was predominantly infected by Laminarionema elsbetiae.