Many aspects of coral reefs remain puzzling to scientists. One mystery

Many aspects of coral reefs remain puzzling to scientists. One mystery concerns the relationship between Scleractinia, the coral type whose colonization produces reefs, and their symbiotic partners, a unicellular algae present in the coral's endodermic tissues. It is known that both organisms play an integral part in the formation of a reef's foundation by together secreting and depositing calcium carbonate, which reacts with sea salt to form a hard limestone underlayer. Scientists also know that, because of algal photosynthesis, the reef environment is oxygen-rich, while similarly high amounts of carbon dioxide are removed rapidly. All of this accounts for the amazing renewability of coral reefs despite the erosion caused by waves. The precise manner in which one symbiotic organism stimulates the secretion of calcium carbonate by the other, however, remains unclear.

In addition to the above unanswered question, scientists have proposed various theories to explain the transformation of "fringing reefs" (those connected above sea level to land masses) into "barrier reefs" (those separated from shorelines by lagoons) and finally into island atolls. Although Darwin's view of the transformation is considered partially correct, some scientists feel that the creation of reef formations has more to do with the rise in sea level that occurred at the end of the last Ice Age than with a gradual submergence of the volcanic islands to which fringing reefs were originally attached. However, recent drillings at one atoll have revealed a substantial underlayer of volcanic rock, which suggests that Darwin's explanation may be largely correct. The term "coral reef" is something of a misnomer. The Scleractiniathemselves generally comprise only 10 percent of the total mass of life forms of an average reef community: algae, along with foraminifera, annelid worms and assorted molluscs, can account for up to 90 percent of the reef mass. Moreover, the conditions under which reef growth occurs are determined by the needs of the algae, not those of the coral. Reefs flourish only in shallow, highly saline waters above 70° F, because the algae require such an environment. Non-reef-building coral, meanwhile, occur worldwide.

1. It can be inferred from the passage that Darwin

A. believed that reefs became atolls through the sinking of volcanoes.
B. should have expanded his studies of reefs to include those found at atolls
C. theorized that each reef was formed by an entirely different process.
D. is less persuasive on the topic of reef formation in light of recent discoveries
E. was more interested in algae and coral than in other organisms living at reefs



2. The passage does NOT discuss the relationship between

A. algal photosynthesis and high oxygen content
B. Darwin's views and evidence supplied by recent research
C. volcanic rock and the life forms found at reefs
D. sea salt and calcium carbonate
E. wave action and the renewal of reefs