A Fijian reef explodes in color as a school of anthias swims past. If a soft coral hosts zooxanthellae (the algae that give coral the nutrients it needs to grow) and the water becomes too warm, the algae leave and the soft coral die. Unlike hard corals, soft corals don’t leave a limestone skeleton behind and cannot regenerate.
Photograph by Tim Laman

Appearing as flowers of the sea, the tentacles of an orange cup coral reach out in the waters of the Caroline Islands in Micronesia. Known for their brilliant colors, these corals inhabit the shallow areas of coral reefs.
Photograph by Heather Perry

A diver explores an emerald kingdom in New Zealand’s Wet Jacket Arm marine reserve. Black coral creates an undersea forest for colorful reef fish and can live for 300 years. Aiding its marine ecosystems by creating reserves, New Zealand hopes to protect 10 percent of its waters by 2010.
Photograph by Brian J. Skerry

Fast Facts
Type: Fish
Diet: Herbivore
Average lifespan in the wild: More than 60 years
Size: Up to 10 ft (3 m)
Weight: Up to 650 lbs (295 kg)
Group name: School
Did you know? The largest freshwater fish ever recorded was a Mekong giant catfish caught in northern Thailand in 2005. It was nearly nine feet long (2.7 meters) and weighed 646 pounds (293 kilograms).

Mekong Giant Catfish Profile
The world’s largest scaleless freshwater fish lives a tenuous existence in the murky brown waters of Southeast Asia’s Mekong River. Capable of reaching an almost mythical 10 feet (3 meters) in length and 650 pounds (295 kilograms), Mekong giant catfish live mainly in the lower half of the Mekong River system, in Cambodia, Laos, Thailand, and Vietnam.Once plentiful throughout the Mekong basin, population numbers have dropped by some 95 percent over the past century, and this critically endangered behemoth now teeters on the brink of extinction. Overfishing is the primary culprit in the giant catfish’s decline, but damming of Mekong tributaries, destruction of spawning and breeding grounds, and siltation have taken a huge toll. Some experts think there may only be a few hundred adults left.Mekong giant catfish have very low-set eyes and are silvery to dark gray on top and whitish to yellow on the bottom. They are toothless herbivores who live off the plants and algae in the river. Juveniles wear the characteristic catfish “whiskers,” called barbels, but these features shrink as they age.Highly migratory creatures, giant catfish require large stretches of river for their seasonal journeys and specific environmental conditions in their spawning and breeding areas. They are thought to rear primarily in Cambodia’s Tonle Sap Lake and migrate hundreds of miles north to spawning grounds in Thailand. Dams and human encroachment, however, have severely disrupted their lifecycle.International efforts are underway to save the species. It is now illegal in Thailand, Laos, and Cambodia to harvest giant catfish. And recently in Thailand, a group of fishers pledged to stop catching giant catfish to honor the king’s 60th year on the throne. However, enforcement of fishing restrictions in many isolated villages along the Mekong is nearly impossible, and illicit and bycatch takings continue.

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

Appearing as solitary forms in the fossil record more than 400 million years ago, corals are extremely ancient animals that evolved into modern reef-building forms over the last 25 million years.
Coral reefs are unique (e.g., the largest structures on earth of biological origin) and complex systems. Rivaling old growth forests in longevity of their ecological communities, well-developed reefs reflect thousands of years of history (Turgeon and Asch, in press).

Corals and their KindCorals are anthozoans, the largest class of organisms within the phylum Cnidaria. Comprising over 6,000 known species, anthozoans also include sea fans, sea pansies and anemones.
Stony corals (scleractinians) make up the largest order of anthozoans, and are the group primarily responsible for laying the foundations of, and building up, reef structures.
For the most part, scleractinians are colonial organisms composed of hundreds to hundreds of thousands of individuals, called polyps.