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  3. CROWN-OF-THORNS STARFISH AND CORAL REEFS (1) The crown-of-thorns starfish, Acanthaster planet, is large, 25 to 35 centimeter

CROWN-OF-THORNS STARFISH AND CORAL REEFS (1) The crown-of-thorns starfish, Acanthaster planet, is large, 25 to 35 centimeter

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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.
Which of the following is NOT mentioned in paragraph 3 as a consequence of the destruction of an area of coral by Acanthasters?
选项 A、Algae colonize the dead area.
B、Plant-eating fish increase in number.
C、Coral larvae disappear.
D、Species diversity recovers fully over time.
答案C
解析 本题要求根据第3段，排除下列哪项不是棘冠海星破坏珊瑚区域引起的后果。原文第3段第3句 “珊瑚幼虫栖息在海藻中，最后建立起繁茂的珊瑚群”说明珊瑚幼虫并不会消失，故C项“珊瑚幼虫消失”不符合原文的说法，符合题意。A项“镣类占领死珊瑚所在的区域”符合原文第3段第1句的说法。B项“食草鱼类的数量增加”符合第3段第2句的说法。D项“物种多样性会随着时间的流逝而完全恢复”符合第3段最后一句的说法。故A、B、D三项都能在原文找到依据，不符合题意，均可排除。
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