决胜六级--简答+改错（5）
Test 5??
Scientists often portray coral reefs as “rainforests of the oceans” for the reason that rainforests and coral reefs are habitats of most species on land and
in seas respectively. However, rainforests grow in nutrient?rich tropics, while
coral reefs lie in nutrient?poor waters. Therefore, how coral reefs manage to
thrive in the marine equivalent of a desert is a subject scientists have been studying. ?
Over the past decade, some scientists have worked out a theory that coral reefs maintain high rates of biological activity by efficiently recycling scarce nutrients. But two U. S. scientists in California are questioning this theory. Robert?
Carpenter of State University in Northridge and Susan Williams of State University in San Diego put forward the idea that long?spined black sea urchins may play a key role in enabling coral reefs to thrive. ?
The urchins specially feed on the algae which live on the coral. By doing so, they may greatly enhance the flow of dissolved nutrients, enabling the algae to maintain high rates of photosynthesis and nitrogen fixation. Carpenter and Williams have gathered a large quantity of data over the past ten years in laboratory studies and field surveys at St Croix in Virgin Islands. However, they are reluctant to challenge the recycling theory headon. ?
Their findings are interesting enough to have attracted funding for them to continue their work at a research station in Kaneohe Bay on the island of Oahu in
Hawaii. They will try to discover to what extent the movement of water, rather