Ocean animals in U.S. zoos and aquariums

Life in salt water

By volume, the oceans provide about 90% of the living space on Earth. Marine life spans everything from microscopic plankton to whales 33 m (108 ft) long, and new species are still being described at a rate of about 2,300 a year.

Ocean animals live in very different ways. Some, like the moon jelly, spend their adult lives drifting with the current in coastal waters. Others, like the harbor seal and the king penguin, hunt at sea but come ashore to rest and breed.

The main ocean habitats

Coral reefs are among Earth's most diverse ecosystems. They cover less than 0.1% of the ocean's area, about half the size of France, yet shelter at least a quarter of all marine species. The clownfish lives among the stinging tentacles of host sea anemones on Indo-Pacific reefs, while the blue tang prefers exposed outer reefs and channels with strong currents.

Shallow coastal waters are just as important. The lined seahorse grips seagrass, floating seaweed and mangrove roots from Nova Scotia's southern waters to Venezuela. The cownose ray moves through estuaries such as the Chesapeake Bay in summer, and the southern stingray can keep breathing while lying flat on the sea floor or half-buried in sediment.

Cooler coastal and subantarctic seas are home to seals, sea lions and penguins. Marine mammals are an informal group united only by their reliance on the ocean. Seals and sea lions are semiaquatic: they spend most of their time in water but return to land to mate, breed and molt. The California sea lion is an eared seal with visible ear flaps and large front flippers, while the harbor seal is a true seal with no external ears.

Pressures on marine life

Commercial hunting drove several marine mammals to extinction, including the Steller's sea cow and the Japanese sea lion. After hunting ended, some species recovered, but about 23% of marine mammal species are still threatened today, meaning they fall in one of the three threatened categories of the IUCN Red List. Bycatch in fishing nets, ship strikes, pollution and underwater noise all add pressure. Some harbor seal populations, for example, have been reduced by disease and conflict with people.

Coral reefs are in steep decline. Shallow tropical reefs have declined by 50% since 1950, threatened by warming and acidifying water, excess nutrients, overfishing and harmful land use, including polluted runoff. Rising sea temperatures cause coral bleaching, which can kill the coral if conditions don't improve.

Fishing pressure reaches beyond reefs. Overfishing drove the cownose ray onto the IUCN list as Vulnerable in 2019, and because it matures late, its numbers recover slowly. Invasive species are a growing problem too: the red lionfish, native to the Indo-Pacific, became invasive along the U.S. East Coast and across the Caribbean after aquarium fish were released.