The rush is on for silky sharks (Carcharhinus falciformis) and yellowtail snappers (Ocyurus chrysurus) to get their share of food tossed out of a dive boat into Cuba's coastal waters. Aggressive and considered dangerous to humans, the silky shark is nevertheless fished for human consumption. Its meat is eaten fresh or salted. Its skin is processed for leather. The fins are sold in the Asian shark-fin trade, and its liver—high in vitamin A—is extracted for medicinal liver oil. Photograph by David Doubilet

Moving as one, a school of sweetlips explores the waters of Australia's Great Barrier Reef. Sweetlips are often accompanied by the cleaner wrasse, a fish that grooms them and keeps their skin and mouths free of infection-causing parasites. Photograph by David Doubilet

 A Cape fur seal (Arctocephalus pusillus pusillus) undulates in rhythm with fronds of kelp in the waters off Gansbaai, South Africa. Although the animals are clubbed during hunts and die when entangled in fishing nets, they are top predators in the region and among the most abundant fur seals in the world. Photograph by David Doubilet

In a world of clouds and crystalline blue, a pair of stingrays glides just below the surface in the waters of French Polynesia's Tuamotu archipelago. The creatures find safe haven here under the protection of one of UNESCO's Man and Biosphere reserves. Photograph by David Doubilet