Sandy Sediment Distribution on Coral Reefs and Beaches at Several Islands of the Ryukyu Island Arc

Abstract

In the Ryukyu Island Arc, bioclastic sands containing foraminifera, e. g. Baculogypsina and Calcarina with spines on their tests, are abundant in sands of beaches and reefs. Attrition of the spines of Baculogypsina and Calcarina clarifies habitat and dispersion of these foraminifera at Yoshihara reef in Ishigakijima, where water flow clearly exists due to a distinct channel in the reef flat. At Sesokojima reef where no distinct channel exists, the method of using the attrition of spines on these bioclastic sands is applicable for evaluating transport courses of the bioclastic sands. This method provides a clue to elucidate gain and loss of beach sands in reefal coasts of the Ryukyu Island Arc.