Streblonema (Ectocarpales, Phaeophyceae) infection in the kelp Laminaria saccharina (Laminariales, Phaeophyceae) in the western Baltic

Abstract

The brown alga Laminaria saccharina is the dominant subtidal macroalga in Kiel Bay, western Baltic. It is infected by the microscopic brown alga, Streblonema aecidioides. Infected thalli may show symptoms of Streblonema disease, i.e. alterations of blade and stipe, ranging from dark spots to heavy deformations and completely crippled thalli. Samples taken from a single locality all year round show that (i) the host population is infected at a high rate of 87±13% (SD), but that (ii) a considerable proportion of thalli containing Streblonema does not show disease symptoms, and that (iii) juvenile hosts, which mainly appear in autumn, are infected at almost the same rate. Thus the infection seems to occur early in the host's life. Juveniles in nature show fewer symptoms of the disease than adults. Two months after infection, oxygen production and growth in laboratory-raised experimentally infected juvenile hosts was not different from uninfected controls. Experimental thalli showed more severe morphological alterations than uninfected controls only four months after infection. Both field and laboratory observations indicate that a lag phase exists between infection and outbreak of the disease.