Ecological studies on the littoral attaching micro-algae. XI. Allelopathic effect of mucilage released from a brown alga Sargassum horneri on marine diatoms.

Abstract

Antialgal (allelopathic) activity of the mucilage excreted by a brown alga Sargassum horneri to various diatom species was examined. The growth of all diatoms examined was completely in-hibited by the crude mucilage at the concentrations, 3->30%, depending on the species. The lag phases of growth of these diatoms were influenced at the lower concentrations, however, their maximum growth rates were not affected at these concentration levels. The sensitivity of each diatom to the mucilage was related ot its ecological status (eiphyte or plankter), that is, epiphytic diatoms were generally more resistant than planktonic ones. But taxonomical difference (Pennales or Centrales) was not related to the sensitivity. The antialgal substances contained in the mucilage were non-dialyzable (>M. W. 25000) and heat-stable. The epiphytic diatom flora on S. horneri seems to be influenced by the allelochemicals pyoduced by their host.