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

[rezbipul]

Coral reefs are one of the most fragile, biologically complex, and diverse marine ecosystems on Earth. This ecosystem is one of the fascinating paradoxes 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. 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, hosts, and even for other members of the reef community. This symbiotic process allows organisms in the reef community to use sparse nutrient resources efficiently.
Unfortunately for coral reefs, however, 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 by-products 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 threatening reef communities sensitive to subtle changes in nutrient input to their waters.

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）
(E) Waste by-products result in an increase in nutrient input to reef communities.

PLEASE EXPLAIN THE ANSWER.

[M98Ranger]

The passage first introduces the coral reef as a kind of self-contained ecosystem that works "symbiotically" with certain types of algae to support life in water that is "clear"...and thus nutrient poor ("clear" refering to the fact that it doesn't have floaties in the water as much as other less "clear" water does).

After this, it introduces a problem that is threatening the Coral Reef ecosystem. Namely, humans moving in and pooping in the nice clean "clear" water...(hopefully the pooping is done indirectly through a toilet, but you never know). The extra "CRUD" in the water causes the delicate balance between the algae and the amount of stuff in the "clear" water to become disrupted to the point where something dies. Once one animal in a symbiotic relationship dies, the other dies. And thus if Algae dies, Coral dies, little fishy that lives in coral dies, shark that eats little fishy dies....etc.

I hope that helped.

[ominous]

i think its the option C...its bcoz clear waters are beneficial for this particular ecosystem to survive...

[vinuharan]

i think the answer is E

coral Reef cannot survive in nutrient rich water.waste by products increase the nutrients in the water.

[vackamania]

its E only..

here is the quote from the passage which supports it ..

Unfortunately for coral reefs, however, 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 by-products all increase nutrient loads in these waters.

hope this solves ur problem ..