Okinawa, largest of the Ryukyu Islands southwest of Japan, is adjacent to a convergent plate boundary. Its geology is complex; influences include volcanism, sedimentation and metamorphism. Near center on Okinawa’s west-facing shore, a cape juts out between two bays fronted by coral reefs. Tucked into the rocky shoreline, this small horseshoe-shaped cove is popular with scuba divers. Despite the cove’s strong currents and depth (to 30 m/99 ft), the sediment reflects nearby reef biodiversity.

Forams abound: the “star sand” Calcarina; two seed-shaped species; chain-like variety near 7 o’clock; the white ruffled disc is likely Marginopora. Glassy white branches and rough chunks are reef corals. The purple U-shape is a kind of octocoral. Echinoderm remains include urchin skeletal plates near center and lower right. Urchin spines represent rock burrowers (black, tan), as well as long-spined reef dwellers (white & brown). The small white spiral below center is a calcified operculum from a turban snail; also present are tube worm coils and bits of crab exoskeleton.