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Coral reefs are one of the most fragile, biologically
complex, and diverse marine ecosystem on Earth. This
ecosystem is one of the fascinating paradoxes of the bio-
sphere: how do clear, and thus nutrient-poor, waters sup-
(5) port such prolific and productive communities? Part of the
answer lies within the tissues of the corals themselves.
Symbiotic cells of algae known as zooxanthellae carry out
photosynthesis using the metabolic wastes of the coral
thereby producing food for themselves, for their corals,
(10) hosts, and even for other members of the reef community.
This symbiotic process allows organisms in the reef com-
munity to use sparse nutrient resources efficiently.
Unfortunately for coral reefs, however, a variety of
human activities are causing worldwide degradation of
(15) shallow marine habitats by adding nutrients to the (water.
Agriculture, slash-and-burn land clearing, sewage disposal
and manufacturing that creates waste by-products all
increase nutrient loads in these waters. Typical symptoms
of reef decline are destabilized herbivore populations and
(20) an increasing abundance of algae and filter-feeding animals.
Declines in reef communities are consistent with observa-
tions that nutrient input is increasing in direct proportion to
growing human populations, thereby threatening reef com-
(25) munities sensitive to subtle changes in nutrient input to
their waters.
1. The passage is primarily concerned with
(A) describing the effects of human activities on algae in
coral reefs
(B) explaining how human activities are posing a threat
to coral reef communities
(C) discussing the process by which coral reefs
deteriorate in nutrient-poor waters
(D) explaining how coral reefs produce food for
themselves
(E) describing the abundance of algae and filter-feeding
animals in coral reef areas
2. The passage suggests which of the following about coral
reef communities?
(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.
3. The author refers to "filter-feeding animals" (line 20)
in order to
(A) provide an example of a characteristic sign of reef
deterioration
(B) explain how reef communities acquire sustenance
for survival
(C) identify a factor that helps herbivore populations
thrive
(D) indicate a cause of decreasing nutrient input in
waters that reefs inhabit
(E) identify members of coral reef communities that rely
on coral reefs for nutrients
4. According to the passage, which of the following is a
factor that is threatening the survival of coral reef
communities?
(A) The waters they inhabit contain few nutrient
resources.
(B) A decline in nutrient input is disrupting their
symbiotic relationship with zooxanthellae
(C) The degraded waters of their marine habitats have
reduced their ability to carry out photosynthesis
(D) They are too biologically complex to survive in
habitats with minimal nutrient input.
(E) Waste by-products result in an increase in nutrient
input to reef communities.
5. It can be inferred from the passage that the author
describes coral reef communities as paradoxical most
likely for which of the following reasons?
(A) They are thriving even though human activities
have depleted the nutrients in their environment.
(B) They are able to survive in spite of an over-
abundance of algae inhabiting their waters.
(C) They are able to survive in an environment with
limited food resources.
(D) Their metabolic wastes contribute to the degra-
dation of the waters that they inhabit.
(E) They are declining even when the water sur-
rounding them remains clear.
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