Ecological studies on the littoral attaching micro-algae. VII. Adhesive strength of epiphytic diatoms on various seaweeds.

Abstract

Epiphytic diatoms on the natural seaweeds (seven brown-algae, two red-algae and one green alga) were fractionated by the five step separating treatments of shaking and rubbing. The order of adhesive strength of diatom species was determined from the recovery patterns of each diatom obtained through the five step separating processes. On the basis of the order, epiphytic diatoms were grouped into four, those are, the group of the smallest adhesive strength (group I) consisting of rather planktonic diatoms and large benthic diatom, group II consisting of fairly large and active motile species, group III which was attaching tightly to substrate or was small non-activemotile diatom, and the group of the largest adhesive strength (group IV). Group IV was com-posed of Cocconeis spp., Gomphorsema sp. and Achnanthes sp. The adhesive strength of epiphyticdiatom would have close connection with its cell size and form, motility, and mucous secretion. The cell number of epiphytic diatom on various seaweeds were 106-108 per gram dry weight. The dominant and subdominant species were Navicula sp., Cocconeis spp., Gornphonema sp., Nitzschia closterium and Synedra tabulata. The species compositions of epiphytic diatom on the different seaweeds were very similar to each other. However, those on Sargassum horneri which excreted extracellular mucus vigorously was particular, that is, Gomphonema sp, occupied more than ninety percent of total epiphytes.