The domino effect
In the 1700-1800s on the coast of California, the sea otter was hunted for its gorgeous pelt. It was killed by fishermen who thought the otters were eating too many of the fish they wanted to catch. The sea otter were hunted almost to extinction. Without the sea otter, fishermen began to see changes in the ecosystem. Sea otters eat sea urchins. When the otters disappeared, the sea urchin population rapidly increased. There were soon more sea urchins on the California coast than ever before. Sea urchins eat kelp. Now that there were so many sea urchins, they ate all the kelp. Kelp is used as a nursery by many types of fish. This set off a chain reaction. With the otters gone and the sea urchins numbers growing quickly, the kelp beds began to disappear. Then the fish, with no safe place to have their young, also began to disappear. In just a few years, the fishermen noticed that the fish were suddenly gone. The ecosystem of the kelp forest, just like all other ecosystems, is a cycle. In the Pacific Coast of North America there are “kelp forests” which are composed of very large brown algae. These are consumed by sea urchins, which are, in turn, eaten by sea otters. When sea otter populations are reduced as a result of hunting and being preyed upon by killer whales, the sea urchin populations can overpopulate and graze down most of the kelp, creating “urchin barrens.” Urchins are very harmful when they overpopulate: they move in packs across the ocean floor and can destroy as much as 30 feet of kelp forest a month. When they are not controlled by otters, their populations can explode and basically destroy the kelp forest by eating enormous amounts of kelp. When population control of prey by their predators then affects the next trophic level, the kelp, it is referred to as a “trophic cascade.” Kelp is vitally important to the ecosystem: they can slow coastal erosion and absorb carbon dioxide from the atmosphere. In a paper published in the October issue of Frontiers in Ecology and the Environment, environmental studies professor Chris Wilmers found that if otters spanned the entire planet, the ultimate growth in kelp forests as a result would remove 10 percent of the carbon dioxide from the atmosphere. If sea otters die out and urchins overpopulate, kelp will disappear and would not be able to remove harmful carbon dioxide from the atmosphere. Therefore, as an ultimate result of sea otter removal from kelp forests, global warming would intensify.