100. Read the following passage, then answer the question below.

Coral reefs cover less than one percent of the ocean floor, yet they shelter roughly a quarter of all marine species. Their productivity rests on a partnership. Reef-building corals are animals, but their tissues host microscopic algae called zooxanthellae. The algae use sunlight to make sugars, much of which the coral absorbs as food, while the coral supplies the algae with shelter and certain nutrients. When seawater stays unusually warm for several weeks, this arrangement breaks down. The algae begin to produce compounds that damage the coral's cells, and the coral expels them. Without its pigmented partners, the coral turns white, a condition known as bleaching. A bleached coral is not dead, but it is starving, and if the warm spell lasts, it may die within weeks.

For years, scientists assumed that bleaching spelled the end of a reef. Recent surveys, however, have shown more variation than expected. Some reefs have recovered within a decade, and a few species have proved remarkably resistant. Researchers have identified several possible explanations. Certain corals host heat-tolerant strains of algae, either from birth or after switching partners. Others live in areas where daily temperature swings are large, which seems to train them to cope with stress. Reefs that are not weakened by pollution or overfishing also recover faster, since healthy fish populations keep fast-growing seaweed from smothering young coral.

These findings have prompted debate about conservation. Some scientists propose moving heat-tolerant corals to damaged reefs; others warn that such interventions treat symptoms and distract from reducing the emissions that cause warming. The disagreement is less about what works than about what should come first.

The author's attitude toward the earlier assumption that bleaching ended a reef's life is that it was