雅思阅读 25: When Reefs Start to Dissolve（当珊瑚礁开始消融）

改编自 Proceedings of the Royal Society B（2026年3月）。雅思阅读 Section 3 难度，约 1050 词。 素材来源：https://royalsocietypublishing.org/rspb/article/293/2066/20253084/480714/Beyond-bleaching-collapse-of-net-coral-reef

Reading Passage

A. Coral bleaching has become, over the last three decades, the most familiar disaster image in marine science. A reef, once a tangle of brown, green and living colour, turns bone-white; the symbiotic algae that give corals their food and their pigment are expelled; and, if the heat passes soon enough, the colour returns and the colony recovers. The 2023–2024 marine heatwave, the fourth global bleaching event on record, was different. It lasted too long, it reached too far across the Pacific, the Caribbean and the Indian Ocean, and — as a study published in Proceedings of the Royal Society B in March 2026 shows — it did more than bleach. It flipped reefs in the tropical eastern Pacific from ecosystems that build limestone into ecosystems that tear it down. The change, measured across eleven reefs off the Pacific coast of southern Mexico, was not a gradual decline spread over years. It was a sudden crossing of a line, measured over a single season, that turned a reef system from a net creator of rock into a net destroyer of it.

B. The line is a number called the carbonate budget. A healthy reef is a factory. Reef-building corals, together with coralline algae that cement the rubble together, extract dissolved calcium carbonate from seawater and lay it down as skeleton, year after year, constructing the complex three-dimensional structure that shelters fish, breaks storm waves and supports coastal fisheries for the villages behind them. The same reef, however, is also being slowly eaten away: parrotfish scrape at it to feed on algae, sea urchins bore into it, worms excavate burrows, and the chemistry of the seawater itself, now more acidic as it absorbs carbon dioxide, dissolves it. The carbonate budget is the difference between what is built and what is eroded. On a healthy reef, the balance is positive, with limestone accumulating at a few kilograms per square metre per year. On a dying reef, it tips into the red — and once erosion outpaces growth, the structure starts to crumble from within, a process that can take a reef from a forest of coral to a rubble plain within a single human lifetime. The villages behind such a reef lose, at the same time, the fish that feed them and the breakwater that shields them from storm surges.

C. The Mexican Pacific reefs studied by Medellín-Maldonado and colleagues sit in Huatulco National Park, along the western edge of the Gulf of Tehuantepec. Their limestone framework is overwhelmingly the work of one genus, Pocillopora, which contributes roughly ninety-five per cent of the reef's carbonate; other corals such as Pavona and Porites contribute only in deeper water. In early 2023, sea surface temperatures across the tropical Pacific began to climb. The anomalies developed before El Niño was formally declared, but the later arrival of the climate phenomenon amplified a heatwave that had already begun. Temperatures peaked in August 2023 at 2.24 degrees above the long-term average; degree heating weeks — a standard measure of cumulative thermal stress, in which each week spent more than a degree above the maximum monthly mean is counted — reached sixteen, far above the thresholds at which bleaching and mortality become inevitable. The Mexican Pacific bleaching alert went out in May; widespread mortality followed by July, and divers found reefs that had been colourful a year earlier reduced to white skeletons draped in algae.

D. The numbers, once the surveys were done across all eleven reefs, were stark. Regional coral mortality exceeded 76 per cent, and on some reefs every living coral was gone. The effect on the carbonate budget was equally dramatic. Before the heatwave, the eleven reefs had been accumulating calcium carbonate at a mean rate of about 4.25 kilograms per square metre per year — productive, but not exceptional. After the heatwave, the same reefs were losing carbonate at roughly 2.67 kilograms per square metre per year. In barely one season, a reef system had crossed from construction into destruction. Worse, the study found that both halves of the budget had been thrown out of joint. The builders — the fast-growing Pocillopora corals, the species that make good on a reef's growth promise — had died back hardest, leaving slow-growing, low-cover species in their place. At the same time, the eroders, having an empty, dead structure to work on, accelerated. The result was not merely a slower reef; it was a reef that was actively dismantling itself, with the limestone framework that had taken centuries to grow dissolving back into the sea.

E. The significance extends well beyond southern Mexico. The Huatulco reefs were not chosen because they were unusual; they were chosen because they were typical. They are dominated, like so many reefs around the world, by a single fast-growing genus whose contribution to the carbonate budget is disproportionate to its cover, and they were exposed to the same combination of a prolonged marine heatwave and an El Niño amplification that affected reefs from the Great Barrier Reef to the Seychelles. If preliminary surveys from those other regions show the same sign-flip, as they appear to, then the world may be looking at a planetary-scale transition in which the majority of tropical reefs have become net sources of limestone rather than sinks. The consequences for the 500 million people who depend on reefs for coastal protection and protein are not abstract: a reef that erodes provides less fish, offers less storm surge protection, and cannot be regrown on any useful timescale, because the slowest-growing corals that rebuild structure need cool, stable decades to recover. Bleaching, as the authors note, was never really the headline. The headline is the day the building stops.

Questions 1-4

Choose the correct heading for paragraphs B, C, D and E from the list of headings below.

List of Headings i. What the surveys found — and the sign that flipped ii. The 2023 heatwave and how it built up iii. Why bleaching is only part of the story iv. The maths of reef construction and destruction v. The history of Pocillopora as a genus vi. Why the findings matter beyond Mexico vii. The role of parrotfish in fishing

1. Paragraph B: ____
2. Paragraph C: ____
3. Paragraph D: ____
4. Paragraph E: ____

Questions 5-8

Choose the correct letter, A, B, C or D.

5. What is a "carbonate budget"? A. The cost of building a limestone aquarium. B. The difference between carbonate laid down by reef organisms and carbonate eroded. C. The total weight of fish caught on a reef. D. A government fund for reef conservation.

6. What was the peak sea-surface temperature anomaly in August 2023? A. 1.0 degrees above average. B. 2.24 degrees above average. C. 22.4 degrees above average. D. It was below average.

7. How did the carbonate budget change after the heatwave? A. It stayed positive but smaller. B. It shifted from positive accumulation to net erosion. C. It rose to 76 per cent. D. It was unaffected.

8. Why did the effects fall hardest on Pocillopora? A. It is the main frame-builder and was bleaching-sensitive. B. It is a slow-growing deep-water species. C. It is the main eroder on the reef. D. It was absent from the Huatulco reefs.

Questions 9-13

Do the following statements agree with the claims of the writer?

Write:

• TRUE if the statement agrees with the information
• FALSE if the statement contradicts the information
• NOT GIVEN if there is no information on this

9. The 2023 event was the fourth global coral bleaching event on record.
10. El Niño began before the sea-surface temperature anomalies developed.
11. Some reefs in the study lost all their living coral.
12. The Mexican government spent $100 million on reef restoration after the event.
13. Reefs that erode still provide the same coastal protection as healthy reefs.

Questions 14-15

Complete the summary below using NO MORE THAN TWO WORDS from the passage.

After the heatwave, the reefs shifted from being carbonate producers to being net (14) __________; the study suggests that bleaching itself is less alarming than the day the (15) __________ stops.

答案与解析

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