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  3. Coral reefs are one of the most fragile, biologically complex, and diverse m

Coral reefs are one of the most fragile, biologically complex, and diverse m

游客2025-02-26  38
问题     Coral reefs are one of the most fragile, biologically complex, and diverse marine ecosystem on Earth. This ecosystem is one of the fascinating para- doxes of the biosphere: how do clear, and thus nutrient-poor waters support such prolific and productive communities? Part of the answer lies within the tissues of the corals themselves. Symbi- otic cells of algae known as zooxanthel-lae carry out photosynthesis using the metabolic wastes of the coral thereby producing food tor themselves, for their corals, hosts, and even for other mem- bers of the reef community. This symbiotic process allows organisms in the reef community to use sparse nutrient resources efficiently.
    Unfortunately for coral reefs, how- ever, a variety of human activities are causing worldwide degradation of shallow marine habitats by adding nutrients to the water. Agriculture, slash-and-burn land clearing, sewage disposal and manufacturing that creates waste byproducts all increase nutrient loads in these waters. Typical symptoms of reef decline are destabilized herbivore populations and an increasing abundance of algae and filter-feeding animals. Declines in reef communities are consistent with observations that nutrient input is increasing in direct proportion to growing human populations, thereby threat- ening reef communities sensitive to subtle changes in nutrient input to their waters. [br] The passage suggests which of the following about coral reef communities?
选项 A、Coral reef communities may actually be more likely to thrive in waters that are relatively low in nutrients.
B、The nutrients on which coral reef communities thrive are only found in shallow waters.
C、Human population growth has led to changing ocean temperatures, which threatens coral reef communities.
D、The growth of coral reef communities tends to destabilize underwater herbivore populations.
E、Coral reef communities are more complex and diverse than most ecosystems located on dry land.
答案 A
解析 文中指出哪点关于珊瑚礁的说法是正确的?A．正确。珊瑚礁群落在营养水平较低的水体中更易生存。文中L5—8的问句已明确指明。另外第二段说：富营养化水体中珊瑚不易生存，也可取非得本选项。B．珊瑚礁群落需要的养分只存在于底层水中。无。C．“ocean temperatures”文中无。D．珊瑚礁的增加威胁植食性物种。造成此种威胁的是人类活动。E．文中未把珊瑚礁和陆上生物群落做比较。
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