Killing Earth’s largest organism

Julian Cribb, Science Alert 10 Jan 08;

Five times in the history of life on Earth, the corals have died out. Each time they have taken tens of millions of years to evolve anew from simpler creatures.

Leading Australian marine scientist Dr J.E.N. “Charlie” Veron argues we are at the brink of a sixth mass extinction – and that the killers of the largest living organism on the planet, the Great Barrier Reef, will be none other than ourselves.

In “A Reef in Time”, published by Harvard University Press, Dr Veron traces the story of the GBR from beginning to what he sees as its probable demise towards the end of the present century.

Charlie Veron is no Hanrahan, crying “We’ll all be rooned”. As former Chief Scientist at the Australian Institute of Marine Science and author of one of the world’s best known reference books on coral species, his is a voice that speaks with calm authority about a subject he has known intimately as a diver and professionally as a scientist for all his working life.

But it is a voice with a tinge of despair, doubting that even humans with our well-honed instincts for self-preservation, can draw back from the planetary chaos we have already unleashed: “It cannot rationally be doubted that we are now at the start of an event that has the potential to become the Earth’s sixth mass extinction. This time there are no bolides (asteroids), no supervolcanoes, and no significant sea level changes...it is a case of humans changing the environment.”

As diver and researcher Charlie sees the Reef as Nature’s pinnacle of achievement in the ocean realm, a place of endless beauty that has endured when other places on Earth have changed beyond recognition. It is the only living organism large enough to be viewed from outer space. What a tragedy if it were reduced to a crumbling, weed-infested heap of limestone rubble within the lifespan of our children, never to return while humans still exist.

The processes that may bring this about are already at work beneath the ocean’s impassive countenance. Invisible eddies of heated water bring sudden death to vast tracts of corals when they linger over them for a few days. And, molecule by molecule, the carbon dioxide we produce each time we start out cars, turn on our lights or produce our goods dissolves into the upper oceans, turning them ever so slightly acid – and acidity is death both to corals and the calcareous algae that ‘glue’ the reef together.

Attempting to reconstruct what many scientists now fear will be the likely fate of the GBR and, indeed, all the earth’s corals (along with the 500 million people they support), Veron reaches back in time to understand the processes that obliterated corals in the ancient past.

At points 434 million, 350 million, 251 million, 205 million and 65 million years before the present, some cataclysm either totally or partially obliterated all the corals on earth, along with a great many other species. For ten million years or more following each event the fossil record is devoid of corals – and of the vast limestone formations, even entire mountain ranges, which they produced. After events like the “Great Dying” at the end of the Permian era (251my ago), it appears corals, along with 96 per cent of all marine life, were totally obliterated and had to begin evolving again from scratch.

The causes of these mass extinctions are unclear, though asteroids, supervolcanoes, tectonic and climate change figure large among the theories. One of the unifying factors may have been the mobilisation of vast amounts of the Earth’s stored carbon into the atmosphere, and thence into the oceans, turning them acid and shutting down the life which depends on alkaline water to form its shells and skeletons. It is possible that the initial great die-off was followed by vast blooms of bacteria, feasting on the carcases, and this in turn stripped all the oxygen from the water (as it does today in highly polluted waters), killing fish and other creatures which had survived the initial acidity.

“The prospect of ocean acidification is frightening,” Veron states. “It is serious because of commitment – a word that will soon be used with increasing frequency in the scientific literature.” Commitment, essentially, means that a process is unstoppable. If the oceans turn acid – as they are already doing - the only known process to reverse this is the slow weathering and dissolution of limestone mountain ranges into the sea over millions and millions of years. The public, aware of the role of CO2 in climate change, is far less conscious of its function in acidifying the oceans and of the vast spans of time required for recovery, suggested by the gaps in the fossil coral record.

Unlike coral bleaching, which is visible 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,” he says. If global atmospheric CO2 levels reach 650-700 parts per million, as they are forecast to do by the latter part of this century, traces of human-produced CO2 will still be present in 30,000 years time, contributing to acidification. This indicates the immense lags in the system even were we to cease burning fossil fuels forthwith.

“Ultimately, and here we are looking at centuries rather than millennia, the ocean’s pH will drop to a point where a host of other chemical changes, including a lack of oxygen, may kick in. We have set the stage for the sixth great mass extinction, and another few decades like our last century will see the Earth committed to a trajectory from which there will be no escape. A continued business-as-usual scenario of CO2 production will ultimately result in destruction of marine life on a colossal scale.”

The need for action to quell CO2 is urgent but Veron – along with other scientists – is frustrated that the media, in its quest for “balance” by including both scientific and non-scientific claims in stories, helps to keep the public and governments in a perpetual state of indecision. “Such public uncertainty, in combination with pressure from groups with vested interests, has prolonged government inaction in democratic countries (notably the USA and Australia) and this delay is already having far-reaching consequences. The GBR will be among the first in a long line of dominoes to fall....”

“A Reef in Time” is an alarming, but not alarmist, book. Passionate yet objective, Veron presents the science behind his argument lucidly: much of this will be new to lay audiences unacquainted with the more recent thinking about climate science. He acknowledges doubt and uncertainty where they exist. Like many, he sees an urgent global effort to eliminate CO2 emissions as fast as possible, using all the scientific and technological firepower at our disposal, as the only possible option.

In the end, however, A Reef in Time is a threnody to the passing of one of the Earth’s most wondrous organisms.

Julian Cribb is an adjunct professor of science communication at the University of Technology Sydney and editor of www.sciencealert.com.au.

Details:

A Reef in Time
J.E.N.Veron
Harvard University Press 2008
ISBN-13:978-0-674-12679-7