2012年大学英语六级快速阅读冲刺题（8）
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Our Endangered Oceans Before anyone can honestly care how important it is to protect marine habitats（生活环境）, one needs to appreciate the vast quantities of marine life that exists in the ocean. It is hard for some people to relate to something they never see. However, it makes sense that the vast expanse of water and its inhabitants, covering 70% of the planet, affects us all. Most marine animals are found near coral reefs. These colorful underwater forests naturally spring to mind with the mention of scuba（水中呼吸器）diving or underwater life. Coral reefs are constructed by living plants and animals, primarily corals that surround their small anemone (海葵)-like tentacles in a hard skeleton that forms much of the reef structure. 考试用书 They generally occur in clear, tropical or semi-tropical seas to a depth of approximately 100 meters (328 feet). Coral reefs fringe approximately one sixth of the world’s coastlines and are the biologically richest of all shallow-water marine ecosystems. They support as many as 1 million species of animals and plants, but only a small fraction have been described. Among the best known groups are at least 5,000 species of fish, over 10,000 species of mollusk (软体动物) and more than 800 species of reef-building corals. Corals are not only important to fish. Reefs are important to the human population for a wide variety or reasons: for one, they are a food source. A majority of people make their living fishing near coral reefs and an even larger part of population enjoys eating some of the catch. Unfortunately, if current trends of over-fishing continue, and we deplete fisheries as fast as we are, then this food source will eventually run out. Scientific evidence shows that 90% of top predators in the ocean are now extinct because of over-fishing-predatory fish include anything salmon sized and above all the way through sharks. On the other hand, killing off the grazing species of fish at reefs allows algae to build up, which in turn kills the coral. With 30% of oceanic fish making their home near coral reefs at one time or another, reefs are essential in maintaining a healthy fish population and many of the fish maintain the coral in return. Sustainable fishing is a must. Corals aren’t only a food source. There is also a clear connection between tsunamis（海啸）and storm events having a much greater impact on eroding coastlines than healthy ones. Healthy reefs protect coastlines from the damage of massive waves. During the recent tsunami in Indonesia, for example, coastlines protected by reefs and mangrove forests remained intact and experienced much less impact than coasts that did not have reefs. Pollution is a major threat to the ocean. Pollution comes in many forms and shapes, but most have one thing in common: Almost all ocean pollutants stem from land based human activity. Waste produced on land eventually finds its way to the ocean. It is not uncommon to find beaches littered with plastic bags and bottles that finally came to rest on shores. Rivers carry dirt, oils, sewage and chemicals out to sea. Garbage also finds its way to ocean. Seeing plastic bags floating around the water instead of fish is not a pretty sight. Washed up garbage on the sand will definitely ruin a nice beach vacation. With many third-world countries relying on tourism for income, it is important to maintain the ocean and beaches in as pristine a condition as possible. Chemicals are constantly absorbed by the ocean. Chemicals have a drastic effect on fish populations and the fishing industry. Chemicals absorbed by animals at sea will also harm the human population that consumes them. Mercury is a chemical now commonly found in larger predatory fish such as tuna and shark. It occurs naturally in the environment and also can be released into the air through industrial pollution. Mercury falls from the air and can accumulate in streams and oceans. Bacteria in the water cause chemical changes that transform the mercury into methylmercury. It is this type of mercury（水银, 汞） that can be harmful to unborn babies and young children. Fish absorb the methylmercury as they feed in these waters. Methylmercury builds up in the tissue of some types of fish and shellfish more than others depending on what the fish eat. High levels of mercury can poison the human body, have adverse effects on the nervous system and prevent a baby from developing normally in the womb. This is just one of the harmful chemicals that are actively absorbed by the ocean. Those of us who enjoy the occasional tuna salad sandwich or swordfish steak have been absorbing natural and industrial chemicals from the meat for a few years now suffer a lot. 中 华 考 试 网 Another chemical pollutant is carbonic acid. Atmospheric CO2 is absorbed by the ocean and reacts with the seawater to form carbonic acid-this makes the ocean more acidic and intolerable to a variety of species. The shells of living mollusks have even been known to dissolve in very acidic areas of the ocean. Sea creatures such as corals, shell fish, sea urchins and star fish are likely to suffer the most because higher levels of acidity makes it difficult for them to form and maintain their hard calcium carbonate (碳酸钙) skeletons and shells. For example, even under the ’low’ predictions for future carbon dioxide emissions into the atmosphere, the combined effects of climate change and ocean acidification mean that corals could be rare on tropical and subtropical reefs, such as the Great Barrier Reef, by 2050. 相关资料 |
