Although the shrimplike crustaceans known as krill are usually less than 2 inches (5 centimeters) in length, their importance to animal life, particularly around Antarctica, is very large. Fish, birds, squids, seals, and penguins are some of the animals that depend on krill for their food supply. Baleen whales may capture more than a ton of these small pinkish creatures in just a few minutes. Scientists believe there are more than 80 different species, or types of krill. They live in open oceans throughout the world.

Physical features

Like other crustaceans, krill have a hard covering known as an exoskeleton. A krill molts—sheds its outside covering—many times as it grows. Its body is transparent (see-through). Krill use their many legs for swimming and gathering food. Most krill have special organs on their lower side that give off light, making them visible at night.

Behavior

Krill swim together in large groups known as swarms. Some swarms are so packed that the area of the Antarctic Ocean through which they are swimming looks pink. Krill spend much of their time deep in the ocean away from enemies. At night they go to the water's surface to feed on simple plants. Some kinds of krill also eat tiny animals. Krill are able to go without eating for months at a time.

Female krill produce about 1,000 eggs each summer. Newborn krill, known as larvae, slowly move from the depth at which they hatched toward the water's surface. The larvae pass through nine stages of development in a period of about two years before reaching adulthood. This process is known as metamorphosis.

Human impact

Fishermen catch krill to use as a shrimp substitute and as animal feed. Krill caught for people to eat must be processed quickly because after the animal dies it builds up a large amount of fluoride, which in high doses is harmful to humans.

Some biologists think the total population of krill may weigh 5 billion tons or more. Although this may sound like a huge number, it might not be when one thinks about how many animals eat krill. Thus, scientists worry about the number of krill being caught by humans and about possibly harmful environmental changes such as rising water temperatures from global warming. If krill populations decrease, so might the populations of the animals that eat them.