在连续不断的漂白事件后，珊瑚礁的死亡和侵蚀部分。科学家周二称，格雷格·托达（Greg Torda）/法新社悉尼（Agence France-Presse Sydney）-澳大利亚大堡礁上的珊瑚在海水温度上升的漂白作用下幸存下来，它们对下一年的另一轮高温环境有更强的抵抗力，这是新兴市场的“一线希望”。与生态系统抗争。联合国教科文组织世界遗产名录所列的位于澳大利亚东北海岸的2300公里长的暗礁在2016年和2017年遭到了背靠背的漂白处理。当异常的环境条件，如温暖的海水温度，导致珊瑚排出微小的光合藻类，使它们失去颜色时，就会发生漂白。如果水温下降，藻类能够重新繁殖，珊瑚就能恢复。在史无前例的连续事件中，珊瑚片死亡或受损，特别是形状像桌子的更易受热量影响的分支珊瑚。但詹姆斯库克大学（James Cook University）的特里休斯（Terry Hughes）教授一直在领导对漂白珊瑚的调查，他在《自然气候变化》（Nature Climate Change）上发表的最新研究中发现，珊瑚礁的反应在这两年中有所不同。”休斯说：“2017年，我们惊讶地发现漂白现象有所减少，因为气温比去年更为极端。”珊瑚礁的北部在2016年受到了最严重的影响，去年漂白程度“少得多”，尽管一些珊瑚礁在两个夏季都经历了类似的热应力水平。研究人员说，在中部地区，尽管2017年的热暴露量更高，但观察到这两年的漂白水平是相同的。同时，在受影响最小的南部地区，第一年轻微漂白的珊瑚在第二年没有漂白。”休斯说：“这让我们大吃一惊，因为如果南部珊瑚在第二年和第一年的表现一样，我们应该看到它们中有20%或30%的珊瑚漂白，而它们没有。”所以他们第一年的经历似乎使他们更加坚强，使他们在第二年的热暴露中适应了中等水平的环境。休斯说，现在说珊瑚礁——世界上最大的生物结构——是否会在邻近昆士兰州的春季热浪过后，在2019年初遭受另一次漂白事件的袭击还为时过早。法新社
A dead and eroding section of reef following back-to-back bleaching events. GREG TORDA/AGENCE FRANCE-PRESSE

SYDNEY - Corals on Australia's Great Barrier Reef that survived bleaching from rising sea temperatures were more resistant to another bout of hot conditions the following year, scientists said on Tuesday, a "silver lining" for the embattled ecosystem.

The 2,300-kilometer-long UNESCO World Heritage-listed reef off Australia's northeastern coast was hit by back-to-back bleaching in 2016 and 2017.

Bleaching occurs when abnormal environmental conditions, such as warmer sea temperatures, cause corals to expel tiny photosynthetic algae, draining them of their color.

Corals can recover if the water temperature drops and the algae are able to recolonize them.

Swathes of coral died or were damaged in the unprecedented successive events, particularly the more heat-susceptible branching corals that are shaped like tables.

But Professor Terry Hughes of James Cook University, who has been leading the surveys of bleached corals, found in the latest study, published in Nature Climate Change, that the response of the reef was different between the two years.

"We were astonished to find less bleaching in 2017 because the temperatures were even more extreme than the year before," Hughes said.

The northern part of the reef, which was worst-affected in 2016, bleached "much less" last year even though some of the reefs underwent similar levels of heat stress in both summers.

In the central regions, the levels of bleaching for both years were observed to be the same, even though the heat exposure was higher in 2017, the researchers said.

Meanwhile, in the southern region - the least-affected - corals that suffered minor bleaching in the first year showed no bleaching in the second.

"That surprised us, because if the southern corals had behaved the same way in year two as in year one, we should have seen 20 or 30 percent of them bleach, and they didn't," Hughes said.

"So it looks like the history of their experience in year one has toughened them up so that they've acclimatized to moderate levels in year two of heat exposure.... It's something of a silver lining."

Hughes said it was too early to say whether the reef - the world's largest living structure - could be hit by another bleaching event in early 2019, after a spring heat wave in adjacent Queensland state.

Agence France-Presse

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