by Tim Flannery
As a result, all over the world people who had hitherto been sheltering in huts and living hand to mouth independently began to grow crops, domesticate animals and live in settled towns. It’s hard to avoid the feeling that the hostile ice-age climate and its savage transition to the interglacial had until then stymied this great flowering of creativity and complexity.11 Indeed, researchers from the University of California at Davis have recently argued that until some 10,000 years ago extreme cold, low levels of CO2 and great climatic variability made it impossible to grow crops.12 Then things changed, and only now have we been able to plumb the causes of our recent good fortune.
2050: The Great Stumpy Reef?
2005
I went upon the reef with a party of gentlemen, and the water being very clear round the edges, a new creation, as it was to us, but imitative of the old, was there presented to our view. We had wheat sheaves, mushrooms, stags horns, cabbage leaves, and a variety of other forms, glowing under water with vivid tints of every shade betwixt green, purple, brown, and white; equalling in beauty and excelling in grandeur the most favourite parterre of the curious florist.
MATTHEW FLINDERS, VOYAGE TO TERRA AUSTRALIS, 1814
OF ALL THE ocean’s ecosystems, none is more diverse nor—as you might guess from the above remarks—more replete with beauty of colour and form than a coral reef; and none, the climate experts and marine biologists tell us, is more endangered by climate change. I’ve heard this alarming opinion expressed at conferences, and am always struck by the dumb response of the audience to such shocking news. It’s as if they either cannot believe it, or the inevitability of bequeathing a world without such wonders to their children puts the matter beyond contemplation.
Can it be that the world’s coral reefs really are on the brink of collapse? It’s a question of considerable self-interest to humanity, for coral reefs yield around US $30 billion in income each year, mostly to people who have few other resources. Financial loss, however, may prove to be a small thing compared with the loss of the ‘free services’ that coral reefs provide. The citizens of five nations live entirely on coral atolls, while fringing reefs are all that stand between the invading sea and tens of millions more. Destroy these fringing reefs, and for many Pacific nations you have done the equivalent of bulldozing Holland’s dykes.
One of every four inhabitants of the oceans spends at least part of their life cycle in coral reefs. Such biodiversity is made possible by both the complex architecture of the corals, which provide many hiding places, and the lack of nutrients present in the clear, tropical water.
Interestingly, low levels of nutrients can promote great diversity. Consider that in regions with fertile soils and abundant rainfall, only a few plant species can dominate. They are the ‘weedy’ ones—those that grow most rapidly given optimum sunlight, water and nutrients—and which can thus out-compete the rest. In contrast, where soils are poor, niche specialists—plants that can thrive only within very narrow limits—proliferate, each of which grows best only where specific nutrients are present in specific amounts, and where rain falls at specific times. The best example of this is seen on the infertile sand plains of South Africa’s Cape Province, where 8000 species of shrubby flowering plants co-exist in a mix as diverse as that of most rainforests.
The coral reefs are the marine equivalent of South Africa’s sand plain flora. And so we can see that nutrients, and disturbances that break down the structure of coral reefs, are the arch-enemy of their diversity, for then only a few weedy species—mostly marine algae—would proliferate.
When Alfred Russel Wallace sailed into Ambon Harbour in what is now eastern Indonesia in 1857, he saw:
one of the most astonishing and beautiful sights I have ever beheld. The bottom was absolutely hidden by a continuous series of corals, sponges, actiniae, and other marine productions, of magnificent dimensions, varied forms, and brilliant colours. The depth varied from about twenty to fifty feet, and the bottom was very uneven, rocks and chasms, and little hills and valleys, offering a variety of stations for the growth of these animal forests. In and out among them moved numbers of blue and red and yellow fishes, spotted and banded and striped in the most striking manner, while great orange or rosy transparent medusae floated along near the surface. It was a sight to gaze at for hours, and no description can do justice to its surpassing beauty and interest.1
During the 1990s I often sailed down Ambon Harbour, yet saw no coral gardens, no medusae, no fishes, nor even the bottom. Instead, the opaque water stank and was thick with effluent and garbage. As I neared the town it just got worse, until I was greeted with rafts of faeces, plastic bags, and the intestines of butchered goats.
Ambon Harbour is just one among countless examples of coral reefs that have been devastated over the course of the twentieth century. Today, the prevalent practice of overfishing—including fishing with explosives and poisons—threatens reef survival, for the stability of coral reefs in the face of climate change utterly depends on the diversity of fishes and other creatures they shelter.2 Disturbing reef biodiversity can also lead to outbreaks of plague species, such as the crown of thorns starfish. Another problem is the runoff of nutrients from land-based agriculture and polluted cities that has helped place most of the world’s reefs under threat. Even protected places such as Australia’s Great Barrier Reef are becoming severely degraded, in this case from a fourfold increase in nutrient and pollution-rich sediments derived from croplands and which the intense El Niño events and tropical cyclones characteristic of our new climate carry far out to sea.3
Climate change-induced damage to reefs sometimes comes from unexpected quarters. The 1997–98 El Niño saw the rainforests of Indonesia burn like never before, and for months the air was thick with a smog cloud rich in iron. Before those fires, the coral reefs of southwestern Sumatra were among the richest in the world, boasting more that 100 species of hard corals, including massive individuals over a century old. Then, late in 1997 a ‘red tide’ appeared off Sumatra’s coast. The colour was the result of a bloom of minute organisms that fed on the iron in the smog.4 Known as dinoflagellates, the toxins they produced caused so much damage it will take the reefs decades to recover, if indeed they ever do.
The smog cloud generated over South-East Asia during the 2002 El Niño was even larger than that of 1997–98—it was the size of the United States. On such a scale smog can cut sunlight by ten per cent and heat the lower atmosphere and ocean, all of which causes problems for corals.5 Dinoflagellate blooms are now devastating coastlines from Indonesia to South Korea and causing hundreds of millions of dollars worth of damage to aquaculture. The prospect of recovery for any east Asian coral reefs looks dimmer than ever.6
It’s the direct impact of higher temperatures, however, that is proving to be the most threatening aspect of climate change to coral reefs. High temperatures lead to coral bleaching, and to understand that phenomenon we need to examine a reef far from human interference, where warm water alone is causing change. There are, thankfully, some reefs protected by remoteness and size, with no pollution, fishermen or tourists. Myrmidon Reef, lying far off the coast of Queensland, sees almost nothing of humans. Every three years scientists from the Australian Institute of Marine Science in Townsville survey it, and when they did so in 2004 they took along environmental writer James Woodford. He described Myrmidon as looking ‘as though it’s been bombed’. This was the result of the reef crest being severely bleached, leaving a forest of dead, white coral. Only on the deeper slopes did life survive.7
Coral bleaching occurs whenever sea temperatures exceed a certain threshold. Where the hot water pools the coral turns a deathly white. If the heating is transient the coral may slowly recover, but when the heat persists it dies. The phenomenon represents the dissolution of a partnership, for the organisms that make up the world’s reefs and atolls are in fact two living things in one. The larger partner in this ecological merger is a pale, sea-anemone-like creature known as a polyp. It
gains its greenish, red or purplish hue from a lodger—a type of algae known as zooxanthellae. Under normal circumstances the relationship is a happy, symbiotic one: the coral polyp provides a home and some nourishment to the algae, while the algae provides the polyp with food from photosynthesis. As the temperature of the seawater rises, however, the algae’s ability to photosynthesise is impaired, and it costs the polyp more to maintain its partner than it gets in return. As in many a failing relationship, this unequal situation leads to a split, though precisely how the polyp ejects the algae (if it does not leave under its own volition) remains a mystery. If temperatures remain high for a month or two, without their algae the polyps starve to death, leaving a skeletal reef that will eventually become overgrown with soft corals and green algae.
Coral bleaching was little heard of before 1930, and it remained a small-scale phenomenon until the 1970s. It was the 1998 El Niño that triggered the global dying. Some coral reefs were studied intensively both before and after this event, which taught scientists a great deal. In the Indian Ocean, the Scott and Seringapatam reefs were severely affected with bleaching to a depth of thirty metres. Prior to 1998, the percentage of hard coral cover on these reefs was a healthy 41 per cent, then dropped to 15 per cent. On Scott Reef there has been a complete failure of coral recovery since; Seringapatam is recovering slowly.
The Great Barrier Reef is the most vulnerable reef in the world to climate change and, due to higher temperatures near the coast and the debilitating impact of pollution, the corals growing nearer the shoreline were harder hit than those on the outer reef. In all, 42 per cent of the Great Barrier Reef bleached in 1998, with 18 per cent suffering permanent damage. In 2002, with the renewal of El Niño conditions, a pool of warm water around half a million square kilometres developed over the reef. This triggered another massive bleaching event that on some inshore reefs killed 90 per cent of all reef-forming corals, and left 60 per cent of the Great Barrier Reef complex affected. In the few patches of cool water that remained, however, the coral was undamaged.
A survey conducted in 2003 revealed that live coral cover had dropped to less than 10 per cent on half of the reef’s area, with large declines evident even in the healthiest sections. Public outrage made political action inevitable, and the Australian Government announced that 30 per cent of the reef would be protected. This meant that commercial fishing would be banned, and other human activities severely curtailed, in the newly protected zone. But it is not fishing or tourists that are killing the reef, that is being done by spiralling CO2 emissions.
Australians emit more CO2 per capita than any nation on Earth. If the Australian Government was truly serious about saving the reef, it would take action in both energy policy and international engagement. Instead, in 2004 the government released its long-awaited energy policy, which enshrined coal at the centre of the nation’s energy generation system.
In 2002 a panel of seventeen of the world’s leading coral-reef researchers warned in an article in Science that ‘Projected increases in CO2 and temperature over the next fifty years exceed the conditions under which coral reefs have flourished over the past half-million years’. By 2030, they say, catastrophic damage will have been done to the world’s reefs, and by 2050 even the most protected of reefs will be showing massive signs of damage.8 The message was reinforced in October 2002 when fifteen of the world’s greatest authorities on coral reefs met in Townsville, Queensland, to discuss the plight of the Great Barrier Reef. According to reef scientist Dr Terry Done a further rise of 1°C in global temperature would see 82 per cent of the reef bleached; 2°C increase 97 per cent, and 3°C ‘total devastation’.9 Because it takes the oceans around three decades to catch up with the heat accumulated in the atmosphere, it may well be that four-fifths of the Great Barrier Reef is one vast zone of the living dead—just waiting for time and warm water to catch up with it.
Extinctions caused by climate change are almost certainly under way on the world’s reefs, and a tiny species of coral reef-dwelling fish known as Gobiodon species C may be emblematic of them.10 Most of the habitat used by this diminutive creature was destroyed by coral bleaching and associated impacts during the 1997–98 El Niño, and it can now be seen only on one patch of coral in one lagoon in Papua New Guinea. ‘Species C’ indicates that it has not yet been formally named, and such is its tenuous situation that extinction may occur before its scientific baptism. We know about Gobiodon species C only because a scientist interested in the genus has spent long months documenting changes in the abundance of this fish that others might not notice. So great is the diversity of coral reefs, and so few are the marine biologists that study them, that it isn’t an exaggeration to say that we need to multiply the loss of this one little fish a thousandfold to gain a sense of the cascade of extinctions that is, in all likelihood, occurring right now.
Yet despite the enormous damage already evident on the world’s coral reefs, some scientists are hopeful that the reefs may yet survive climate change. If we’d been able to visit Australia’s Great Barrier Reef 15,000 years ago, they point out, we would have seen little more than a raised line of limestone hills separating a coastal plain from the sea. At that time every coral reef in existence today was high and dry, for the ocean was 100 metres lower than at present. The major hard coral families that make up the reefs were in existence before the end of the Cretaceous Period sixty-five million years ago, when an asteroid struck the planet and devastated global ecosystems. Just how they survived is unclear, though it was almost certainly only in special refuges. Some scientists think that those survivors altered the chemistry of their skeletons; others argue that, for a time, they did away with skeletons altogether. Corals may be forced to such extremities again in the future, for as CO2 accumulates in the atmosphere and then diffuses into the ocean, it turns the seas acidic and prevents the coral organism from secreting its hard skeleton.
This history suggests it is possible that some individual coral species could survive, while the overall biodiversity of reefs may not. In order to know which conditions the full diversity of coral reefs can tolerate, we need to consider the earliest evidence we have for the life that swarms on today’s reefs. The best place to do this is on a verdant hill called Monte Bolca, near the Italian city of Verona, where finely laminated deposits of limestone packed with the bodies of ancient marine fish have been mined since the sixteenth century.
Fifty million years ago the region around Verona was a lagoon behind a coral reef, and when the reef fish died they were washed into its still waters, where their brilliantly coloured bodies drifted into the oxygenless bottom layers. Without oxygen there can be no decay, and at Monte Bolca the preservation is so exquisite that some of the colour patterns of those long-dead fish can still be seen. Scientists have identified 240 species in the deposits, and among them are the ancestors of many of the fish that inhabit the world’s modern coral reefs. The presence of so many fishes so early in the geological record suggests a rapid radiation of species following a catastrophe. Given what we know of the methane-fuelled climatic cataclysm of fifty-five million years ago, it seems possible that this event devastated earlier coral reef fish—and in all likelihood the reefs themselves—and that in the aftermath the coral reef communities we know today took their place.
There are two ways that the species that constitute coral reefs might survive the looming threat of climate change: by adapting or migrating. Recent research has found that some types of zooxanthellae that live inside the polyps can tolerate higher temperatures than others. One algal form, known as Symbiodinium strain D, is particularly good at tolerating warm water, but because it’s not as efficient at producing food from sunlight as its low-temperature cousins, it is today relatively rare.11 On reefs destroyed by bleaching, however, its abundance has increased. If corals can adapt in this way there is hope that some of them, and perhaps reefs, will survive in the locations where they grow right now.12 Yet the extent of adaptation would need to expand many times
over and occur swiftly to save the majority of coral reefs from devastation.
Another escape route may lie in corals migrating south to cooler waters. In the case of the Great Barrier Reef, the coast south of the coral’s present distribution lacks the extensive shallow continental shelf required to support large reefs. A few species might find refuge in places like Sydney Harbour, but only a fraction of the diversity of even mobile reef species could exist in such limited spaces.
So what is the prognosis for the world’s coral reefs? The complexity of their ecology, and our limited knowledge of key aspects of them, makes the response of the reefs towards warming among the most difficult of climate change outcomes to determine. Nevertheless, the damage already sustained is a strong indication that reefs are sensitive to the perturbations climate change brings, leading me (and many other scientists) to believe that the future for reefs under the emerging new climate is bleak.
Let’s imagine what the Great Barrier Reef might look like fifty years from now. Only fifty of the 400 species of hard coral currently inhabiting the reef complex are likely to have adapted to using Symbiodinium strain D as partners, and almost all of these heat-hardy species are lumpy rocklike forms or thick, sturdy types. Not only are such corals relatively unattractive, but they do not form the labyrinthine structures so necessary to the reef’s biodiversity.13 It is hard to believe that anything more than a small proportion of the reef’s creatures could survive this transformation. So, in effect, visitors travelling to Queensland by 2050 may see the Great Stumpy Reef. Tourism is Australia’s second-largest income earner, and the Great Barrier Reef is one of the industry’s leading drawcards, so deciding who will pay to see the wonders of the Great Stumpy Reef is of more than academic significance. And, with some nations entirely dependent upon coral reefs for their existence, far more than economics is at stake.