雅思阅读 137: The Last Wilderness on the Seafloor（深海热液喷口——最后的荒野）

改编由 PNAS（2024年）。雅思阅读 Section 3 难度，约 1050 词。 素材来源：https://www.pnas.org/doi/10.1073/pnas.2403899121

Reading Passage

A. Two thousand metres below the ocean surface, where sunlight has never reached, plumes of superheated, mineral-rich water erupt through cracks in the volcanic crust. These hydrothermal vents, or "black smokers", look like scenes from another planet. The water issuing from them may exceed three hundred degrees Celsius, laced with toxic sulphides and heavy metals, yet around each vent swarms a dense ecosystem of tube worms, clams and crabs that could not survive anywhere else. The animals do not eat each other in the usual way; they farm bacteria inside their bodies, bacteria that draw energy from the vent's chemistry rather than from the sun. The vents themselves are tiny — the total area of all active vents on Earth is thought to cover only about fifty square kilometres, less than a medium-sized city — yet they are among the most extraordinary habitats on the planet. Until recently they were also one of the least touched. That is now changing, because the metal-rich deposits forming around them are exactly what deep-sea mining companies want. The International Seabed Authority has been negotiating exploitation rules for years, and several nations have already signed exploration contracts over vent-rich ridges in international waters.

B. A global analysis of more than five hundred vent species has set out to measure how resilient these communities would be to disturbance. The results are sobering. Although the vents are scattered across every ocean basin, the species that live there draw on a surprisingly small repertoire of biological strategies. Of thousands of possible combinations of body size, mobility, feeding mode and habitat, only a few score are actually used, and most species cluster along two broad axes: one running from large, rooted, symbiotic foundation species such as the giant tubeworm to small, mobile scavengers, and another running from animals found only at vents to visitors from surrounding deep-sea mud. The harsh chemistry of the vents, it seems, acts as a filter that admits only a narrow set of solutions — which is efficient, but also means there is little backup if one of those solutions is removed. The study's authors found that more than sixty per cent of all trait variation among the five hundred species plotted onto just two dominant axes. The remaining axes captured distinctions between species that live only at vents and those that also roam the surrounding deep-sea mud.

C. The study's most worrying finding concerns functional uniqueness. Across the world's vents, half of all distinct ecological roles are performed by a single species, with no natural substitute waiting in the wings. In some regions the proportion rises above ninety per cent. When the researchers simulated extinctions, they found that removing between a quarter and a half of species was enough to wipe out half of the ecosystem's functional diversity. In other words, because each animal tends to do a job that no other animal does, the loss of even a few species translates directly into the loss of a function. The vents also function as stepping stones: larvae drift from one vent to the next along mid-ocean ridges, so that removing one vent site starves the next of recruits. Knock out enough sites and the whole chain breaks. Most vent species have tiny geographic ranges, often known from one or two individual vents, so a single mining concession can remove a species' entire global habitat.

D. This matters because the mining proposals are not abstract. The ores that mining companies want — polymetallic sulphides rich in copper, zinc and sometimes gold — form precisely on the vents themselves. As environmental groups put it bluntly, on a vent the ore is the habitat. There is no way to extract the deposit without scraping away the animals attached to it, and sediment plumes stirred up by collection vehicles can drift far beyond the mine site, smothering larvae and animals at neighbouring vents. In the only full-scale mining trial of a vent system conducted so far, biodiversity collapsed within the mined area. Even where vents are left untouched, drilling and pipeline work can alter the flow of hot fluids, starving the communities that depend on them. Because most vent species are known from only one or a handful of sites, wholesale removal of those sites means extinction, not local decline. Even the sediment plumes themselves, which can drift for tens or hundreds of kilometres, are a second, invisible form of mining that does not show up on the mine's own boundary. A plume can smother larval recruits at vents that the collector never touches, quietly severing the stepping-stone connections that keep the regional population alive. Even the noise of the mining vessels may disrupt the navigation and communication of deep-diving marine mammals that range far beyond the mine site itself.

E. The researchers' recommendation is precautionary, and it is made against a tight deadline. Restoration, they note, is unlikely to work in such remote, extreme environments; a vent community, once smashed, will not regrow on any human timescale. Yet the same analysis that reveals the risk also reveals the opportunity: vents remain one of the last marine wildernesses, still close to a natural baseline. Protecting them now — through marine reserves, strict environmental review, and a moratorium where the science is weakest — would prevent the kind of extinction that, in more accessible habitats, has already become routine. The vents are small, and they are strange. But they are also one of the few places left on Earth where human impact has not yet rewritten the rules, and deciding what to do with them is, the authors argue, a choice about what kind of planet we want to leave behind. The United Nations Food and Agriculture Organization already lists vent ecosystems as vulnerable marine environments, a designation that stops short of full protection but sets a precautionary tone.

Questions 1-4

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

List of Headings i. Why the vents themselves are the mining target ii. A small repertoire of survival strategies iii. Why vent water is so hot iv. Alarming functional uniqueness and the stepping-stone problem v. How to grow tubeworms in the laboratory vi. A precautionary recommendation before it is too late vii. Why the deep sea is rich in fish

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. How do vent animals obtain energy? A. By eating surface-dwelling fish. B. By farming symbiotic bacteria that use the vent's chemical energy. C. By photosynthesis, like plants. D. By absorbing sunlight through transparent skin.

6. What is notable about the number of functional strategies at vents? A. Thousands of strategies are used by every species. B. Only a narrow range of possible strategies is actually employed. C. Each species invents a completely unique strategy. D. Strategies are identical across all ocean depths.

7. Why is mining the ore at a vent especially damaging? A. The ore lies buried under metres of harmless sediment. B. The ore itself forms the habitat on which vent animals live. C. Mining companies restore the vents afterwards. D. The ore is poisonous to bacteria.

8. What does the "stepping stone" model imply? A. Vents are connected only by submarine cables. B. Larvae move between vents, so removing one site can deprive the next of recruits. C. Mining creates stepping stones for tourism. D. Vent species walk between sites on the seafloor.

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. Hydrothermal vents cover roughly fifty square kilometres in total worldwide.
10. More than half of all distinct ecological roles at vents are performed by a single species.
11. Mining companies have promised to restore mined vent sites within five years.
12. In the only full-scale vent mining trial conducted so far, biodiversity recovered within two years.
13. The giant tubeworm Riftia pachyptila hosts symbiotic bacteria in a specialised organ.

Questions 14-15

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

Because most vent species are known from only one or a few sites, the removal of those sites risks outright (14) __________ rather than merely local decline; the authors therefore urge (15) __________ protection before mining expands.

答案与解析

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