SECTION 2 TIME—25 MINUTES 18 QUESTIONS DIRECTIONS

2.

The passage suggests which of the following about

complex, and diverse marine ecosystems on Earth. This

coral reef communities?

ecosystem is one of the fascinating paradoxes of the bio-

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sphere: how do clear, and thus nutrient-poor, waters sup-

(A) Coral reef communities may actually be more

(5

) port such prolific and productive communities? Part of the

likely to thrive in waters that are relatively low in

answer lies within the tissues of the corals themselves.

nutrients.

Symbiotic cells of algae known as zooxanthellae carry out

(B) The nutrients on which coral reef communities

photosynthesis using the metabolic wastes of the corals,

thrive are only found in shallow waters.

thereby producing food for themselves, for their coral

(C) Human population growth has led to changing

(10

) hosts, and even for other members of the reef community.

ocean temperatures, which threatens coral reef

This symbiotic process allows organisms in the reef com-

communities.

munity to use sparse nutrient resources efficiently.

Unfortunately for coral reefs, however, a variety of

(D) The growth of coral reef communities tends to

human activities are causing worldwide degradation of

destabilize underwater herbivore populations.

(15

) shallow marine habitats by adding nutrients to the water.

(E) Coral reef communities are more complex and

Agriculture, slash-and-burn land clearing, sewage disposal,

diverse than most ecosystems located on dry

and manufacturing that creates waste by-products all

land.

increase nutrient loads in these waters. Typical symptoms

of reef decline are destabilized herbivore populations and