9781422279151

world, which makes their survival very im- portant. Marine mammals play a key part in keeping ecosystems healthy. For one thing, they are larger than most other ma- rine species, so they eat more. This helps keep the populations of smaller animals,

Life of a marine mammal.

such as fish, shrimp, and squid under control. Mammals can also be hosts for other types of life. Barnacles, for ex- ample, are small creatures that attach themselves to the bodies of gray whales. That way, they get a free ride to bet- ter ocean-feeding grounds. The health of marine mammals says a lot about ocean life in general—if they are doing well, then it’s a good bet other marine life is too. Marine mammals fall into four main categories. Ceta- ceans are the main swimmers and include whales, dol- phins, and porpoises. Pinnipeds are another major group that includes seals, sea lions, and walruses. (Seals and sea lions are similar, but sea lions are better adapted for mov- ing around on land.) Manatees and dugongs belong to the sirenia category. They are commonly known as “sea cows,” which is a perfect description for these large, slow-moving animals. Sea otters and polar bears are in the category of marine fissipeds. They have feet and are related to land

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