Global warming and the fate of the world’s coral reefs
by David Adam
Animal, vegetable and mineral, a pristine tropical coral reef is one
of the natural wonders of the world. Bathed in clear, warm water and
thick with a psychedelic display of fish, sharks, crustaceans and other
sea life, the colourful coral ramparts that rise from the sand are known
as the rainforests of the oceans.
And with good reason. Reefs and rainforests have more in common than
their beauty and bewildering biodiversity. Both have stood for millions
of years, and yet both are poised to disappear.
If you thought you had heard enough bad news on the environment and
that the situation could not get any worse, then steel yourself. Coral
reefs are doomed. The situation is virtually hopeless. Forget ice caps
and rising sea levels: the tropical coral reef looks like it will enter
the history books as the first major ecosystem wiped out by our love of
cheap energy.
Today, a report from the Australian government agency that looks
after the nation’s emblematic Great Barrier Reef reported that “the
overall outlook for the reef is poor and catastrophic damage to the
ecosystem may not be averted”. The Great Barrier Reef is in trouble, and
it is not the only one.
Within just a few decades, experts are warning, the tropical reefs
strung around the middle of our planet like a jewelled corset will
reduce to rubble. Giant piles of slime-covered rubbish will litter the
sea bed and spell in large distressing letters for the rest of
foreseeable time: Humans Were Here.
“The future is horrific,” says Charlie Veron, an Australian marine
biologist who is widely regarded as the world’s foremost expert on coral
reefs. “There is no hope of reefs surviving to even mid-century in any
form that we now recognise. If, and when, they go, they will take with
them about one-third of the world’s marine biodiversity.
Then there is a domino effect, as reefs fail so will other
ecosystems.This is the path of a mass extinction event, when most life,
especially tropical marine life, goes extinct.”Alex Rogers, a coral
expert with the Zoological Society of London, talks of an “absolute
guarantee of their annihilation”.
And David Obura, another coral heavyweight and head of CORDIO East
Africa, a research group in Kenya, is equally pessimistic: “I don’t
think reefs have much of a chance. And what’s happening to reefs is a
parable of what is going to happen to everything else.”
These are desperate words, stripped of the usual scientific caveats
and expressions of uncertainty, and they are a measure of the enormity
of what’s happening to our reefs.The problem is a new take on a familiar
evil. Of the billions of tonnes of carbon dioxide spewed from cars,
power stations, aircraft and factories each year, about half hangs round
in the thin layer of atmosphere where it traps heat at the Earth’s
surface and so drives global warming.
What happens to the rest of this steady flood of carbon pollution?
Some is absorbed by the world’s soils and forests, offering vital
respite to our overcooked climate. The remainder dissolves into the
world’s oceans. And there, it stores up a whole heap of trouble for
coral reefs.
Often mistaken for plants, individual corals are animals closely
related to sea anemones and jellyfish. They have tiny tentacles and can
sting and eat fish and small animals. Corals are found throughout the
world’s oceans, and holidaymakers taking a swim off the Cornish coast
may brush their hands through clouds of the tiny creatures without ever
realising.
It is when corals form communities on the sea bed that things get
interesting. Especially in the tropics. Yes, Britain has its own rugged
coral reefs, but such deep-water constructions are too remote, cold and
dark to really fire the imagination. It is in shallow, brightly light
waters, that coral reefs really come to life. In the turquoise waters of
the Caribbean, Indian Ocean and Pacific, the coral come together with
tiny algae to make magic.
The algae do something that the coral cannot. They photosynthesise,
and so use the sun’s energy to churn out food for the coral. In return,
the coral provide the algae with the carbon dioxide they need for
photosynthesis, and so complete the circle of symbiotic life.
Freed of the need to wave their tentacles around to hunt for food,
the coral can devote more energy to secreting the mineral calcium
carbonate, from which they form a stony exoskeleton. A second type of
algae, which also produces calcium carbonate, provides cement.
Together, the marine menage-a-trois make a very effective building
site, with dead corals leaving their calcium skeletons behind as
limestone. For all their apparent beauty and fragility, just think of
coral reefs as big lumps of rock with a living crust.
A fragile crust too. The natural world is a harsh environment for
coral reefs. They are under perpetual attack by legions of fish that
graze their fields of algae.
Animals bore into their shells to make homes, and storms and crashing
waves break them apart. They may appear peaceful paradises, but most
coral reefs are manic sites of constant destruction and frantic
rebuilding. Crucially though, for millions of years, these processes
have been in balance.
Human impact has tipped that balance. Loaded with the agricultural
nutrients nitrates and phosphates, rivers now spill their polluted
waters into the sea. Sediment and sewage cloud the clear waters, while
over-fishing plays havoc with the finely tuned community of fish and
sharks that kept the reef nibbling down to sustainable levels. All of
this is enough to wreck coral without any help from climate change.
Global warming, predictably, has made the situation worse. Secure in
their tropical currents, coral reefs have evolved to operate within a
fairly narrow temperature range, yet, in the late 1970s and 1980s, coral
scientists got an unpleasant demonstration of what happens when the hot
tap is left on too long. “The algae go berserk,” said Rogers.
Scientists think the algae react to the warmer water and increased
sunlight by producing toxic oxygen compounds called superoxides, which
can damage the coral. The coral respond by ejecting their algal lodgers,
leaving the reefs starved of nutrients and deathly white.
Such bleaching was first observed on a large scale in the 1980s, and
reached massive levels worldwide during the 1997-98 El Niño weather
event.
On top of a human-warmed climate, the 1997-98 El Niño, caused by
pulses of warming and cooling in the Pacific, drove water temperatures
across the world beyond the coral comfort zone. The mass bleaching event
that followed killed a fifth of coral communities worldwide, and though
many have recovered slightly since, the global death toll attributed to
the 1997-98 mass bleaching stands at 16%. “At the moment the reefs seem
to be recovering well but it’s only a matter of time before we have
another [mass bleaching event],” says Obura.
With its striking images of skeletal reefs stripped of colour and
life, coral bleaching offers photogenic evidence of our crumbling
biodiversity, and has placed the plight of coral reefs higher on the
world’s consciousness. Head along to your local swimming pool for diving
lessons these days, and chances are that you will be offered a coral
conservation course as well.
Katy Bloor, an instructor at Sub-Mission Dive School in
Stoke-on-Trent, says many divers are not aware of the problems corals
face, particularly as holiday operators tend to visit reefs in better
condition. “Most have probably dived on a coral reef that they thought
was a bit rubbish, but they haven’t considered why,” she said.
If anyone knows what they are missing out on, it should be Charlie
Veron. So what does it feel like to dive on a pristine reef? “I have not
seen many reefs that can be called pristine, and none exist now,” he
says. “But if I had to take a punt, I was diving on the Chesterfield
Reefs, east of New Caledonia [in the southwest Pacific] about 30 years
ago and was staggered by the wealth of life, especially big fish which
were so thick that I was hardly ever able to photograph coral. That
place made even remote parts of the Great Barrier Reef look second rate.
“I can only describe it like walking through a rainforest dripping
with orchids, crowded with birds and mammals of bewildering variety and
trees growing in extreme profusion.”
Can the coral be helped? If planting more trees can regrow a forest,
can coral be introduced to bolster failing reefs? There are a handful of
groups working on the problem, many of which have reported encouraging
results. Off Japan, scientists are farming healthy coral on hundreds of
ceramic discs, which they plan to transplant onto the badly-bleached
Sekisei Lagoon reef within two years. In 30 years or so, they hope the
reef can recover fully.
A similar, if more low-tech, exercise is under way in the Philippine
coastal community of Bolinao, where local people have broken off chunks
from the healthy section of their local reef and have crudely wedged
them into cracks in bleached sections.
Others have cultured corals in swimming pools, and researchers in the
Maldives are using giant sunken cages, connected to a low level electric
current, to help coral form their chalky shells.
But the problem with all these efforts, according to Rogers at the
ZSL, is that they cannot address the looming holocaust that reefs face.
A new, terrible curse that comes on top of the bleaching, the battering,
the poisoning and the pollution.
Remember the carbon dioxide that we left dissolving in the oceans?
Billions and billions of tonnes of it over the last 150 years or so
since the industrial revolution? While mankind has squabbled, delayed,
distracted and dithered over the impact that carbon emissions have on
the atmosphere, that dissolved pollution has been steadily turning the
oceans more acidic. There is no dispute, no denial, about this one.
Chemistry is chemistry, and carbon dioxide plus water has made
carbonic acid since the dawn of time.
As a result, the surface waters of the world’s oceans have dropped by
about 0.1 pH unit - a sentence that proves the hopeless inadequacy of
scientific terminology to express certain concepts. It sounds small, but
is a truly jaw-dropping change for coral reefs.
For reefs to rebuild their stony skeletons, they rely on the seawater
washing over them to be rich in the calcium mineral aragonite. Put
simply, the more acid the seawater, the less aragonite it can hold, and
the less corals can rebuild their structure. Earlier this year, a paper
in the journal Science reported that calcification rates across the
Great Barrier Reefs have dropped 14% since 1990. The researchers said
more acidic seas were the most likely culprit, and ended their sober
write-up of the study with the extraordinary warning that it showed
“precipitous changes in the biodiversity and productivity of the world’s
oceans may be imminent”.
Rogers says carbon dioxide levels in the atmosphere are already over
the safe limits for coral reefs. And even the most ambitious political
targets for carbon cuts, based on limiting temperature rise to 2C, are
insufficient. Their only hope, he says, is a long-term carbon
concentration much lower than today’s.
The clock must somehow be wound back and carbon somehow sucked out of
the air. If not, then so much more carbon will dissolve in the seas that
the reefs will surely crumble to dust. Given the reluctance to reduce
emissions so far, the coral community is not holding its breath.
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