Understanding the Situation Kelp Forests Provide Shelter and Food for a Variety of Marine Species

Investigation 9: Ecoscenarios Monterey Bay National Marine Sanctuary Understanding the Situation Kelp forests provide shelter and food for a variety of marine species. In the past 40 years, the kelp population has declined dramatically in Monterey Bay National Marine Sanctuary. Some of the main factors affecting the kelp population are kelp harvesting, loss of sea otters, and pollution runoff from land farming. Kelp harvesting Kelp is a source of algin, an ingredient that makes foods smooth and creamy. It is used in pudding, salad dressing, icing, gravy, sauces, and milk shakes. Kelp is also used in toothpastes, shampoos, soap, pills, dyes, and paints, making kelp production an important ecosystem service. In the 1800s, kelp farmers wrapped cables around large areas of kelp to pull it up. This also pulled up a lot of other things from the ocean bottom and all the organisms living along the stipe (stem). This prevented the kelp and its surrounding community from growing back quickly. Today, kelp is harvested by cutting the stipes about 1.2 meters below the water’s surface. This way the holdfast (rootlike structure) and most of the stipe remains intact. The kelp regrows quickly and can be cut again later. Some people think that using these new farming techniques does not negatively affect the ecosystem. They point to the example of Norway, where there is a large kelp-harvesting industry. Norway has used scientific research to develop farming techniques that seem to support sustainable kelp populations. Other people are worried that even this type of farming could damage the kelp population or the other populations living around it. The kelp forest ecosystem is complex, so it is hard to know for sure. Currently there is no agreement on the best way to harvest kelp. Keystone species: The sea otter A keystone is a stone used when constructing stone arches. This important stone holds the other stones in place. Similarly, keystone species play an important role in maintaining a community of organisms. Not all communities have keystone species, but for those that do, the loss of that one species can destroy the whole ecosystem. Sea otters are considered the keystone species of the kelp forest, and they have been hunted nearly to extinction. Native Americans hunted sea otters for thousands of years. But when other hunters This graph shows the number of sea otters in Monterey Bay began killing sea otters for fur in the 1700s, sea National Marine Sanctuary from 1900 to 2000. Before sea otter otter populations along the Pacific coast were hunting began in 1741, there were about 20,000 animals here. FOSS Populations and Ecosystems Course, Next Generation Understanding the Situation © The Regents of the University of California Page 1 of 2 Investigation 9: Ecoscenarios Monterey Bay National Marine Sanctuary nearly wiped out. By the 1920s, only one group of sea otters was left south of Alaska. These otters were at Point Sur, California, but their location was kept secret by a small group of researchers. All of the current California sea otters are descended from this group. As otters disappeared, kelp forests also disappeared. Researchers wondered if hunting sea otters was related to the disappearance of kelp forest. They realized that sea otters eat sea urchins. Sea urchins eat kelp. If there aren’t as many sea otters around to eat urchins, then the sea urchin population increases. Sea urchins eat so much kelp that they can create large areas where the kelp is entirely gone. These areas are called urchin barrens. Water-quality control Fertilizers are chemicals that help plants grow. When too much fertilizer is sprayed on a field or a lawn, it runs off into streams and rivers, and these take the runoff to the ocean. Many rivers deposit runoff in the Monterey Bay National Marine Sanctuary. These rivers bring runoff from agriculture (farm) areas to kelp forests. Another kind of runoff comes from urban areas. You have probably noticed large storm drains in the sidewalks in cities. These drains let rainwater run off the streets. The water washes many substances along with it. These substances can include oil and grease from cars; soil, pesticides and herbicides from manicured lawns; and pet droppings. After a rainstorm, they enter the storm drains with the rainwater and flow into Monterey Bay. Runoff from farms and cities ends up in Monterey Bay. One of the problems with this runoff is called nutrient pollution. These nutrients help plants grow, which may sound helpful, but in an ecosystem it can throw things an ecosystem out of balance. In the ocean, extra nutrients like phosphorus can cause overpopulation of algae, called algal blooms. These blooms can block sunlight from the kelp forests and stop the kelp from growing. They also produce toxins (harmful substances) that can threaten the health of humans and the kelp forest ecosystem. Sediments (sand and silt) in runoff can also block sunlight in the ocean and prevent kelp growth. All these sources of pollution are difficult to prevent because they come from many different places. Humans over a large area are affecting the water quality of Monterey Bay. Wikimedia Commons Wikimedia Commons Urban and agricultural pollution Algal blooms block sunlight runs off cities and farmland and and use up oxygen ends up in the bay. underwater. FOSS Populations and Ecosystems Course, Next Generation Understanding the Situation © The Regents of the University of California Page 2 of 2.

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