Marine Animals

Marine animals are those that live in the salt water of the world's seas and oceans, an environment that covers most of the planet's surface. They include an enormous variety of life, from microscopic plankton to the largest animal ever known, the blue whale. Living in water poses challenges of buoyancy, pressure, temperature and the need to obtain oxygen, and marine animals have evolved many solutions, from gills that extract oxygen from water to streamlined bodies that reduce drag while swimming.

Fish are the most numerous marine vertebrates. They breathe through gills, are typically covered in scales, and use fins to steer and propel themselves. Marine mammals, by contrast, are air-breathing animals descended from land-dwelling ancestors that returned to the sea. Dolphins and whales are cetaceans that must surface to breathe and that nurse their young, while seals, including the predatory leopard seal of Antarctic waters, divide their lives between sea and shore. These mammals are warm-blooded and often insulated by thick layers of blubber.

Marine animals form intricate food webs. Tiny drifting plankton support small fish, which in turn feed larger predators such as sharks, dolphins and seals. Many marine species undertake long migrations and depend on healthy habitats such as coral reefs, kelp forests and open ocean. Ocean ecosystems face growing pressures from overfishing, pollution and warming seas, making the study and protection of marine life increasingly important.

Frequently asked questions

Are dolphins and whales fish?

No. Dolphins and whales are marine mammals. They breathe air, are warm-blooded, and nurse their young, unlike fish, which breathe through gills.

How do fish breathe underwater?

Fish use gills to extract dissolved oxygen from water as it flows over them, allowing them to breathe without surfacing.

What is a leopard seal?

The leopard seal is a large predatory seal of Antarctic waters, named for its spotted coat. It hunts penguins, fish and other seals.