Five times in the history of life on Earth, the corals have perished. Each time they have taken millions of years to return or evolve anew. The eminent Australian marine scientist Dr JEN ‘Charlie' Veron argues that we are now on the brink of a sixth mass extinction - and that we will be the killers of the largest living organism on the planet, the Great Barrier Reef.
In A Reef In Time: The Great Barrier Reef from Beginning to End (Harvard University Press, 304pp; $49.95), Veron traces the story of the reef, from its creation more than 25 million years ago to what he sees as its likely death towards the end of the present century. He is no ecological Hanrahan, crying, "We'll all be rooned"; as the former chief scientist at the Australian Institute of Marine Science and the author of one of the leading reference books on coral species, he speaks with calm authority. But his is a voice also tinged with despair, and he questions whether we have the necessary resolve and sense of urgency to stop the chaos we are unleashing.
As a diver and researcher Veron has visited and studied all of the world's significant coral centres of diversity. He regards the Great Barrier Reef as Nature's finest achievement in the realm of the ocean, a place of endless beauty and richness that has endured while other places on Earth have changed beyond recognition. It is the only living organism big enough to be viewed from outer space. It is also the product of a wondrous collaboration, between the corals themselves and algae (zooxanthellae) which turn sunlight into food for the corals, along with other algae which cement their homes together. A coral reef, Veron points out, is less a battleground of competing organisms than a marvel of co-operation and mutual support, in which each species is a member of a "guild" that plays its part in supporting the whole. It is a system that humans can learn from. What a tragedy, then, if within the lifespan of the next generation the Great Barrier Reef - along with all the other coral reefs - was reduced to a weed-infested heap of limestone rubble, never to return while humans exist.
The processes that may cause this are already underway beneath the surface of the ocean. Invisible eddies of overheated water bring a sudden white death, known as bleaching, to vast tracts of corals when they linger over them for a few days. There are already signs that sea levels will rise far faster than corals can grow. Diseases never before seen are rampant. And, molecule by molecule, the CO2 we produce each time we start our cars, heat or cool our homes, or undertake our work dissolves into the upper oceans, turning them ever so slightly acidic. Even mild acidity spells death to corals and the calcareous algae that glue the reef together, as well to as many of the ocean's planktonic organisms, the most numerous creatures on Earth and the main producers of the air we breathe.
In each of the previous mass extinctions, some cataclysm totally or largely obliterated all the corals on Earth, along with a great many other species in the sea and on land. For 10 million years or more following each incident, the fossil record is devoid of corals - and of the vast limestone formations, entire mountain ranges, which they produced. After incidents like the Great Dying at the end of the Permian era (251 million years ago), it appears that corals, along with 96% of all marine life, were wiped out and had to begin evolving again.
The causes of the extinctions are unknown, though asteroid collisions, super-volcanoes, tectonic upheavals and climate change are all possibilities. A likely consequence of any of these would have been the release of vast amounts of the Earth's stored carbon into the atmosphere. This CO2 would dissolve back into the oceans, turning them acidic and ending all life which depended on alkaline water to form chalky shells and skeletons. It is probable that the initial die-off was followed by vast blooms of fungi and bacteria, feasting on the carcasses, which in turn stripped all oxygen from the water (as happens now in highly polluted waters), killing fish, molluscs and other creatures which had survived the initial acidity. Between them, acidity and anoxia would explain the extinction of most sea life.
"The prospect of ocean acidification is frightening," Veron says. "It is serious because of commitment - a word that will soon be used with increasing frequency in the scientific literature." He does not mean something as frangible as a politician's vow, but rather a process that is unstoppable. If the oceans turn acidic, as they are already doing, the only known way of reversing this is the slow weathering and dissolution of limestone mountain ranges into the sea, a process which takes millions of years in gradually getting the water back to its normal alkalinity. Today the public is keenly aware of how CO2 heats the planet, but far less conscious of how it also acidifies the oceans - or of the time, so vividly illustrated by those immense gaps in the fossil record, that it takes the oceans to regain balance.
Unlike coral bleaching, which can be seen within days, acidification is a creeping death. "The long-term outlook is that reefs will be committed to a path of destruction long before any effects are visible," Veron states bluntly. If global atmospheric CO2 levels attain the 650 to 700 parts per million they are forecast to reach by late this century (even if we adopt all the proposed reduction measures), some of this human-generated CO2 will still be around in 30,000 years, acidifying the oceans. Here Veron - and he is not alone among scientists - criticises the media for perpetuating indecision by including both scientific and non-scientific claims in its reporting of climate change, as if they were of equal validity:
Such public uncertainty, in combination with pressure from groups with vested interests, has prolonged government inaction in democratic countries (notably the US and Australia) and this delay is already having far-reaching consequences. The Great Barrier Reef will be among the first in a long line of dominoes to fall ...
A Reef in Time is an alarming, but not alarmist, work. Veron is passionate yet objective, presenting the science behind his argument lucidly and accessibly. Much will be new to lay audiences unacquainted with the latest thinking about climate science, and unaware of how much more grave than the official outlook many eminent scientists consider the situation to be. Veron has chosen an example so graphic that it is hard to ignore. If we kill the Great Barrier Reef, the book insinuates, what would that say of us?
"This account ... may seem like a science-fiction horror story, but there is little evidence of fiction either in the science or in the simplified interpretation I have given," Veron writes. Even so, he continues, there is cause for hope. Enormous reductions in greenhouse emissions will soon be forced on humanity, so we may as well get on with it - and fast. As for the Great Barrier Reef, the first and only step we can take is to cease polluting the Earth with CO2, while minimising all the other stresses to which we subject it. This is the decade in which we must decide, Veron says, and in which we must act. If we do, the corals, though scarred, will probably pull through.
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