A cuttlefish (Sepia sp.) appears to be dozing above a coral reef in Kimbe Bay in Papua, New Guinea. Biologist Simon Thorrold has been working in the area as part of a long-term study of the movement of fish larvae among different reefs in the bay. Cuttlefish are not fish, but cephalopod mollusks related to squid and octopus. Within their fleshy mantle is the cuttlebone, which is made of calcium carbonate and contains many small holes. By changing the amount of gas in the holes, the cuttlefish can change its buoyancy and its depth in the water.
Image credit: Simon Thorrold, Woods Hole Oceanographic Institution