RELATIONSHIP BETWEEN BLOCK DETRITION DEGR EES OF SEA-BOTTOM SEDIMENT (HEDORO), AND GROWTH AND SURVIVAL RATES OF BROWN ALGAL SPROUTS

As a link in the chain of effective utilization programs of sea-bottom sediment (i.e. HEDORO), a survival-type seaweed culturing concrete bl ock (which is hereinafter referred to simply as ''block'') was designe d. The block is quite different from the existing kind, and it has suc h a distinctive feature that a scanty detrition takes place on the blo ck at all times so that its surface could be always renovated. The HED ORO collected from the coastal sea bottom off Tomioka-Machi, Fukushima Pref. consisted of clay and silt, and a volume mean diameter of those composites was 11.3 mum; and its moisture content was 100%. In the wa ter standing still, the detrition degrees of the specimen block mixed with varied Portland cement rates differed one after another, indicati ng that the lower degrees was inversely proportional to the cement rat es from 10% to 50%. For example, the degree showed 9.10 x 10(-6) cm/da y when the cement rate was 10%, and 1.16 x 10(-6) cm/day when it was 3 0%. Any changes in the detrition degree were not observed from 40 days after setting on the blocks in the water. The block detrition degree had not any correlation with the growth rate of gametophyte as well as sporophyte of brown algae Eisenia bicyclis; and such a degree was in inverse correlation to the survival rate of algal sprouts. For instanc e, in case of the higher detrition degree of 6.07 x 10(-6) cm/day, the survival rate of those sprouts on 16 days was smaller showing the val ue of 23.2%; on the contrary, in case of the lower degree of 9.15 x 10 (-7) cm/day, it stood for the larger value of 56.6%.