抄録
The objective of this study was to clarify the difference of light environmental condition between seaweed beds dominated by Sargassum horneri, Sargassum macrocarpum and Ecklonia kurome. Light irradiance inside and outside of the seaweed beds were measured at Hashira-jima island, in Hiroshima Bay, on November 29, 2002. To define the relationship between light environmental condition and biomass, the structure of S. horneri and S. macrocarpum beds were investigated. Light environmental conditions were compared by relative light irradiance normalized surface irradiance. The biomass of E. kurome was largest and S. horneri was smallest among the investigated species in this study. The attenuation of relative light irradiance outside of seaweed beds was exponential and attenuation coefficient ranged between 0.2m^<-1>1 to 0.28m^<-1>. Relative light irradiance in the S. horneri and S. macrocarpum beds also reduced exponentially from top to bottom surface of seaweed beds. The attenuation was clearer in S. horneri than S. macrocarpum. Relative light irradiance at the bottom of E. kurome bed normalized to the irradiance at the top of bed was 3.8%. Relative light irradiance at the bottom surface normalized to the irradiance of top of the S. horneri and S. macrocarpum beds were 9.5% and 13.6%, respectively and larger in S. horneri bed even though the biomass was smaller than S. macrocarpum bed. The attenuation and reduction of light irradiance by macroalgae closely agreed.
