Marine afforestation of the kelp Eisenia bicyclis in coralline flats by introduction of porous-concrete reefs

We designed the new porous-concrete algal reefs that enable abundant reproductive cells of algae to gather up for marine afforestation in coralline flats. Marine algal succession on porous reefs and ordinary-concrete reefs at a depth of 5 m in coralline flats off Oshika Peninsula, Japan was monitored from August 1997 through December 1999. After 10 months, the kelp Eisenia bicyclis grew well on porous reefs with a corrugated surface and 20-13 mm in aggregate diameter, while crustose coralline red algae dominated on the other porous reefs with < 13 mm in aggregate diameter and ordinary reefs. It is considered that development of kelp forests was caused by early colonization of small perennial algae with chemical defensive substances that exclude grazing of the sea urchin Strongylocentrotus nudus. We conclude that porous reefs with large aggregate diameter and a corrugated surface are effective for marine afforestation in coralline flats.