每天一篇經濟學人
「 再忙也不忘充電 」
本次選文：Coral in Asia：Polyp apocalypse
陰暗冰冷的海底世界中，珊瑚礁毫無疑問更像一片仙境：五顏六色的海洋動物遊弋於奇形怪狀的珊瑚叢中，構成了美麗的海中熱帶雨林景觀。
珊瑚礁被視為地球上最古老、最多姿多彩也最珍貴的生態系統之一。
珊瑚的主體是由珊瑚蟲組成的。我們所看到的各式各樣的珊瑚樹，一簇簇像分叉樹枝形狀多樣，樹枝狀、球狀、丫杈狀、條狀、螺旋狀等等，不一而足的東西，其實是許許多多微小而柔軟的珊瑚蟲緊緊相連的群體。
說到珊瑚礁，知名度最高的恐怕就是澳洲大堡礁了。但是從照片上可以看到，大堡礁不少多彩繁盛的珊瑚礁已經變成了僅剩白色骨骼的珊瑚"墳場"。
這個世界上最著名的珊瑚礁，遭受到海水升溫的持續影響，在2016和2017年連續出現珊瑚大量白化的事件。
2016年，海水升溫在大堡礁遠北部和北部造成超過26%和67%的珊瑚死亡。大堡礁中部和南部珊瑚死亡率在2016年相對較低，不過它們並未逃過一劫，2017年的白化出現了進一步的惡化，並且對中部的影響更大（ARC Centre of Excellence for Coral Reef Studies）。為什麼海水升溫會造成這麼嚴重的白化問題？這要從珊瑚的生長環境說起。珊瑚礁主要分布在南北半球海水平均溫度20℃的等溫線內，這是由於形成珊瑚礁的造礁石珊瑚對海水水溫有著嚴格要求，多數造礁石珊瑚生活的適宜水溫是18-29℃。
正是由於蟲黃藻和珊瑚蟲的共生系統維持了珊瑚的生存和生長。
但這個系統又是脆弱的，當海水溫度上升超過正常溫度3-4℃時，珊瑚與蟲黃藻這一對好夥伴就會翻臉，蟲黃藻會離開珊瑚蟲，而珊瑚則因為缺少蟲黃藻提供能量而餓死。
截至2010年，我國廣東、廣西、海南沿岸的珊瑚礁在過去的30年中由於人類活動破壞和汙染導致失去了80%的造礁石珊瑚數量；而南海的珊瑚島礁儘管沒有汙染的影響，但由於漁業的過度捕撈和長棘海星的暴發，在近10-15年珊瑚平均覆蓋率從60%下滑至20%左右。
目前，在全球範圍已經有超過一半珊瑚礁出現嚴重退化，但更嚴重的問題是，珊瑚礁的退化速度在未來還會加快。
如果人類不採取任何挽救措施，那麼依照現在的退化速度，珊瑚礁生態系統可能在本世紀末，就從地球上消失。
珊瑚礁是眾多海洋生物繁衍棲息之地、歷史上無數生命的進化源泉、得天獨厚的科學研究寶庫，被稱為「海底森林」。
近期，數名科學家在英國《自然》期刊上發文表示，如果氣候變暖以目前的速度持續下去，全世界的珊瑚礁到2070年可能會全部消失。
全球變暖引起的海水溫度上升，已導致珊瑚礁發生嚴重的白化，對其生態系統產生了致命性影響。
Coral in Asia：Polyp apocalypseReefs face a deadly onslaught from pollution, overfishing and climate change.Small boats criss-cross Black Rock Reef on their way to nearby seaweed and pearl farms. Below, the blue lips of giant clams open and close amid a jungle of multicoloured coral. At the sound of a distant detonation—dynamite fishing, although illegal, is common in the area—a small shark swims hurriedly away. The reef lies nestled off the town of Taytay, on the island of Palawan in the Philippines. Its vivid blues, pinks and greens are a welcome sight given how many nearby corals died because of unusually warm water almost a decade ago—a blight that is becoming commonplace because of global warming.The outlook for coral is dire. The Intergovernmental Panel on Climate Change, a un body, predicted last month that a rise in global temperatures of 1.5ºC relative to pre-industrial times would probably kill 70-90% of the world's coral reefs. Given that the planet has already warmed by about 1ºC, the countdown for corals has begun. But the diversity of coral species and the variety of habitats in which they thrive mean that they will not disappear in a uniform way. Understanding why reefs like Black Rock survive and recover from overheating is essential to conservation efforts.→Intergovernmental Panel on Climate Change: 政府間氣候變化專門委員會（IPCC）Black Rock lies in the Coral Triangle, 6m square kilometres of water in the heart of South-East Asia that is home to perhaps half of the world’s coral reefs (see map). The Triangle's waters teem with an abundance of life almost unmatched elsewhere on the planet. More than 130m people depend on it for their food and livelihood. The reefs support myriad marine species, and provide a spawning ground for the largest tuna fishery in the world. According to a study involving the United Nations Environment Programme, economic benefits from the Coral Triangle were worth $13.9bn in 2017. Tourism generated 45% of that, and commercial fishing 42%. The rest came from coastal development, which reefs help to protect by acting as buffers against rough seas.Coral consists of symbiotic communities of algae and tiny animals called polyps. The polyps give the coral its structure. This provides shelter to algae; they in turn generate sugars on which the polyps feed. When temperatures rise, the polyps expel the algae, causing coral to lose its colour and die—a process known as bleaching. Temperature is not the only critical variable: corals are also sensitive to factors such as light levels, dissolved chemicals and changing currents.→symbiotic: A symbiotic relationship is one in which organisms, people, or things exist together in a way that benefits them all. 共生的→algea: Algae are plants with no stems or leaves that grow in water or on damp surfaces. 水藻→polyp: A polyp is a small animal that lives in the sea. It has a hollow body like a tube and long parts called tentacles around its mouth. 水螅These sensitivities explain why corals are so vulnerable. In addition to climate change, local stresses still abound. "It's not about managing the reefs, it's about managing the people," says Peter Mumby of the University of Queensland in Australia. In the Philippines some 40m of them live within 30km of a coral reef. Overfishing disrupts reefs' ecosystems. Coastal construction can lead to the dumping of sediment in the ocean, clouding waters and blocking needed light. Mavic Matillano, who works in the Philippines for wwf, a conservation group, worries particularly about how reefs are being affected by road-widening and other construction on Palawan. Run-off from fertilisers and untreated sewage are other nasty problems with which corals must contend.At the same time, the world's oceans are warming. They have absorbed more than 90% of the extra heat produced by humans in recent decades. Between 1985 and 2006 the waters of the Coral Triangle warmed at a rate of 0.2ºC per decade. That might not sound like much, but as a rule of thumb reefs bleach when the temperature of the surrounding waters rises 1ºC above the historical norm for four or more weeks, turning colourful corals into ghostly forests.The most recent global spate of bleaching, in 2014-17, affected perhaps 70% of coral reefs, according to America's National Oceanic and Atmospheric Administration. It was particularly severe because it coincided in part with El Niño, a periodic climate pattern that warms equatorial waters in the Pacific every few years. Even reefs that had not experienced any recent extensive bleaching, such as the northernmost areas of Australia's Great Barrier Reef, suffered badly. Severe bleaching is now occurring too frequently for reefs to recover fully. "We don't know how well the biology can continue to be culled and then bounce back," explains Gregory Asner of Arizona State University. By the middle of the century bleaching may occur every year.→Great Barrier Reef: （澳）大堡礁Climate change threatens reefs in other ways, too. The oceans have absorbed about 30% of the increased flows of carbon dioxide into the atmosphere, becoming less alkaline as they do so. This sets in motion chemical reactions that make it harder for the corals to build their exoskeletons. More intense tropical storms, meanwhile, could see reefs more frequently smashed; rising sea levels could see them drowned.→alkaline: Something that is alkaline contains an alkali or has a pH value of more than 7. 含鹼的; 鹼性的→exoskeleton: the protective or supporting structure covering the outside of the body of many animals, such as the thick cuticle of arthropods 外骨骼; 甲殼Scientists, politicians and activists are trying to tackle both the short-term and long-term threats which corals face. The thinking is that the local environment makes a difference: corals that face fewer local threats may have a better shot at surviving larger changes to their environment. It helps that the number of marine protected areas (mpas) around the world is on the rise. Research suggests that coral cover increases in older, well-enforced mpas in isolated areas. mpas now encompass 8% of the ocean, up from less than 1% two decades ago.Much of the increase is a result of America, France and Britain safeguarding areas around their overseas territories. Countries such as the Cook Islands in the South Pacific Ocean have protected their entire national waters. The Coral Triangle Initiative, an alliance of the six countries in the area, has also promoted mpas. Yet only a tiny share of its members' waters is shielded. The cost and complexity of patrolling mpas remain a huge challenge.In the Philippines a change to the law more than two decades ago transferred control of coastal waters up to 15km offshore to municipal governments. It gives local communities a greater say in how to manage marine resources. Ms Matillano says that talking to mayors and other local officials about the business case for protecting reefs works well, as does including locals in the teams which enforce such protection. She adds that some 155 mpas exist off Palawan, though not all are effective. Wilfredo Licuanan of De La Salle University in Manila, who studies Palawan's reefs, also estimates that only a tiny fraction of coastal towns hire a marine biologist for guidance. He gives talks in shopping malls and at public events to educate Filipinos about the plight of their corals.Meanwhile scientists are racing to discover why some types of coral have recovered from recent bleaching events better than others. The answers may involve adaptation (genetic processes) as well as acclimatisation (non-genetic ones). The intricate work requires data that can be difficult to obtain from areas which lack adequate monitoring. There are big knowledge gaps when it comes to the Coral Triangle, for example.→acclimatization: is the process in which an individual organism adjusts to a gradual change in its environmentTeams in America are looking into selectively breeding and conditioning corals, and expensive coral "gardening" occurs in places that can afford it. This involves transplanting corals to reefs in need, often by placing them on man-made underwater structures on which they can grow. In one area near Taytay, corals cling to sturdy metal frames, and a garden for giant clams has been established.Another way forward could be to identify the most resilient sorts of coral in spots that are most sheltered from changing ocean temperatures and other human harm. That could allow more careful targeting of resources. Work published last year in Conservation Letters by a team led by Hawthorne Beyer of the University of Queensland finds that reefs in parts of the Philippines and Indonesia and off eastern Australia, among other places, may face a less severe threat than those in Hawaii and off western Australia. That is a small spot of good news for Black Rock Reef.--END--