Beach sediments of Isla Perez consist of about 60 per cent Halimeda algae, 25 per cent coral, and 15 per cent foraminifera and others. Six discrete sediment populations are present, distinct in skeletal origin, grain size, grain shape, and position on the island. Large blocks of massive coral occur on the southeast margin, facing the strongest waves. Sticks of staghorn coral make up extensive ramparts chiefly along the south coast, and also form a pavement with sticks oriented perpendicular to shore just below the water line. The most abundant sediment is 0o sand, chiefly discoidal Halimeda segments; superbly sorted 2o sand, chiefly coral grit, blankets the west coast where waves are gentlest. Gastropod fecal pellets form a thick layer at the back ends of two shallow, calm, restricted bays. Carbonate mud, resulting from abrasion of coral and Halimeda, is present in small amounts in the subtidal sediments. All the pure sediment populatons have very similar good sorting values,σranging from 0.3 to 0.6o over...