Marine mucilage in Ariake Sound, Japan, is composed of transparent exopolymer particles produced by the diatom Coscinodiscus granii

Concomitant with the bloom of a diatom, Coscinodiscus sp., there was a sudden production of mucilage in the central area of Ariake Sound during the autumn of 2007. To obtain basic information about this marine mucilage and identify the causative organism, we have examined the morphological characteristics of Coscinodiscus sp. and the production of transparent exopolymer particles (TEPs) by this species. Light and electron microscopy studies revealed that the morphological characteristics of the species under investigation were consistent with previous descriptions of Coscinodiscus granii and, hence, we identified this species as C. granii. Alcian blue staining revealed that the TEPs produced by C. granii were composed of acidic polysaccharides. The properties of these polysaccharides were examined using two fluorescein isothiocyanate (FITC)-labeled lectins: FITC-concanavalin A (Con A), which is specific for d-mannose and/or d-glucose, and Ulex europaeus agglutinin-1 (UEA-1)-FITC, which is specific for l-fucose. The Con A label scarcely reacted with the surface of the marine mucilage produced by C. granii, while UEA-1-FITC showed a strong reaction. These results indicate that the TEPs produced by C. granii contain more l-fucose than d-mannose and/or d-glucose. Such TEPs with high l-fucose content are known to be highly viscous. We conclude, therefore, that the polysaccharide composition of the TEPs produced by C. granii may determine the viscosity of the marine mucilage.