Parts of plant body of Eisenia bicyclis or Ecklonia cava are often torn off due to waves and/or marine animals' gnawing, thus become to drift along sea bottom asdrift algae. The useful Abalone and Sea Urchin eat these drift Algae. But a considerable mass of drift algae will move and is diffused due to wave and tide without being eaten by useful marine animals. Accordingly, in Japan, the development of drift alga trap works has been tried since about ten years ago. The aim of the study is to show a new type of concrete blocks which are suitable for drift alga trap, and also to show the method of disposition and anti-wave design of the blocks.
