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CROWN-OF-THORNS STARFISH AND CORAL REEFS

游客2024-01-02  12
问题                                         CROWN-OF-THORNS STARFISH AND CORAL REEFS
    (1) The crown-of-thorns starfish, Acanthaster planet, is large, 25 to 35 centimeters in diameter, and has 7 to 21 arms that are covered in spines. It feeds primarily on coral and is found from the Indian Ocean to the west coast of Central America, usually at quite low population densities. Since the mid-1950s, population outbreaks at densities four to six times greater than normal have occurred at the same time in places such as Hawaii, Tahiti, Panama, and the Great Barrier Reef. The result has often been the loss of a 50% to nearly 100% of the coral cover over large areas.
    (2) [A] A single Acanthaster can consume 5 to 6 square meters of coral polyps per year, and dense populations can destroy up to 6 square kilometers per year. [B] Acanthasters show a preference for branching corals, especially Acroporids. [C] After an outbreak in a particular area, it is common to find that Acroporids have been selectively removed, leaving a mosaic of living and dead corals. [D] In places where Acroporids previously dominated the community devastation can be almost complete, and local areas of reefs have collapsed.
    (3) Areas of dead coral are usually colonized rapidly by algae and often are later colonized by sponges and soft corals. Increases in abundance of plant-eating fish and decreases in abundance of coral-feeding fish accompany these changes. Coral larvae settle among the algae and eventually establish flourishing coral colonies. In 10 to 15 years the reefs often return to about the same percentage of coral cover as before. Development of a four-species diversity takes about 20 years.
    (4) Two schools of thought exist concerning the cause of these outbreaks. One group holds that they are natural phenomena that have occurred many times in the past, citing old men’s recollections of earlier outbreaks and evidence from traditional cultures. The other group maintains that recent human activities ranging from physical coral destruction through pollution to predator removal have triggered these events.
    (5) One theory, the adult aggregation hypothesis, maintains that most species are more abundant than we realize when a storm destroys coral and causes a food shortage. The adult Acanthasters converge on remaining portions of healthy coral and feed hungrily. Certainly there have been outbreaks of Acanthasters following large storms, but there is little evidence that the storms have caused the enough reef damage to create a food shortage for these starfish.
    (6) Two other hypotheses attempt to explain the increased abundance of Acanthasters after episodes of high terrestrial runoff following storms. The first hypothesis is that low salinity and high temperatures favor the survival of the starfish larvae. The second hypothesis emphasizes the food web aspect, suggesting that strong fresh water runoff brings additional nutrients to the coastal waters, stimulating phytoplankton production and promoting more rapid development and better survival of the starfish larvae.
    (7) Those favoring anthropogenic (human influenced) causes have pointed to the large proportion of outbreaks that have been near centers of human populations. It has been suggested that coral polyps are the main predators of the starfish larvae. Destruction of coral by blasting and other bad land use practices would reduce predation on the starfish larvae and cause a feedback in which increases in Acanthaster populations cause still further coral destruction. Unfortunately, there are too few documented instances of physical destruction of coral being followed by outbreaks of Acanthasters for these hypotheses to be fully supported.
    (8) Another group of hypothesis focuses on removal of Acanthaster predators. Some have suggested that the predators might have been killed off by pollution whereas others have suggested that the harvesting of vertebrate and invertebrate predators of Acanthasters could have reduced mortality and caused increased abundance of adults. The problem with this group of hypothesis is that it is difficult to understand how reduced predation would lead to sudden increases in Acanthaster numbers in several places at the same time in specific years. It seems probable that there is no single explanation but that there are elements of the truth in several of the hypotheses. That is there are natural processes that have led to outbreaks in the past, but human impact has increased the frequency and severity of the outbreaks. [br] Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
选项 A、Blasting and other bad land use practices would cause the destruction of coral and increase the number of predators that feed on Acanthaster larvae.
B、Bad land use practices would reduce predation on Acanthaster larvae and increase the starfish population which would cause more coral destruction.
C、A reduction of bad land use practices would reduce coral destruction by increasing the survival of Acanthaster larvae and their predators.
D、The destruction of coral through land use activities would cause a decrease in the number of predators that feed on Acanthaster larvae.
答案 B
解析 本题考查对文中高亮句子的理解和同义转述，属于句子简化题。原句可定位至第7段第3句，意为“爆破和其他不当的土地利用方式造成的破坏，一方面会减少珊瑚虫对棘冠海星幼虫的捕食，另一方面棘冠海星数量的增长会进一步造成对珊瑚的破坏”。B项“不良的土地利用方式会减少对棘冠海星幼虫的捕食，增加棘冠海星群落，这将导致更多的珊瑚遭到破坏”为原文的同义改写，故为正确选项，A项“爆破和其他不良的土地利用方式将导致珊瑚遭到破坏，并增加以棘冠海星幼虫为食的捕食者的数量”，原文表明“一方面会减少珊瑚虫对棘冠海星幼虫的捕食”，这说明捕食者的数量应该是减少的，而不是增加，故A项信息与原文内容不符。C项“减少不良的土地利用方式将会通过提高棘冠海星幼虫及其捕食者的存活率来减少珊瑚的破坏”，文中并未提及不良土地利用方式减少的信息，属无中生有项。D项 “因土地利用行为导致的对珊瑚的破坏将会导致以棘冠海星幼虫为食的捕食者数量的减少”，虽提及了捕食者数量的减少，但是还缺失了“棘冠海星数量的增长”的相关内容，语义并不完整。
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