UNDERSEA TREASURES
An area of ocean twice the size of India hosts an astonishing array of marine animals and is vital to life in the Indo-Pacific. So why is so little known about the Coral Triangle?
There’s something about cuttlefish I’ve always loved. They take an interest. If you approach them underwater in the right way – slowly, indirectly and with respect – it’s not uncommon for them to investigate you.
Being cephalopods they’re quite intelligent, and they’re inquisitive. So, on a remote reef in the Solomon Islands and in a scene reminiscent of Close Encounters of the Third Kind, there’s contact between distant life forms: mollusc and human. Considering I’m in the cuttlefish’s world, strictly speaking my role in this meeting is as the alien.
Fixing me with an exotically designed eye, the cuttlefish raises two of his arms, extending them forwards in a defensive posture. But he has come to me and so soon he relaxes, subtly changing hue. These animals are known to use waves of colour in their skin to ‘hypnotise’ small prey like crabs – or at least baffle them off guard. Apparently it works, because I am spellbound, eye-to-eye with a cuttlefish.
As a wildlife filmmaker, this is just one of the encounters I have had while diving the reefs of the Coral Triangle. Over the years I’ve done multiple shoots in this location, and with good reason: it’s a spectacular part of the world, home to a vast array of marine life.
The Coral Triangle is the biggest treasure trove of biological diversity probably the fewest people have ever heard of. Bounded by the Philippines in the north, Indonesia in the south-west and the Solomon Islands in the east, the Triangle encompasses nearly six million km2 of sparkling ocean, housing the richest coral reefs in the world.
“THE BIRD’S HEAD PENINSULA HAS 72 PER CENT OF THE WORLD’S CORALS ON ONE HEADLAND.”
It contains six island nations – the remaining three being Malaysia, East Timor and Papua New Guinea. Admittedly, it’s not a shape Pythagoras would have been proud of, but nonetheless picturing it requires distinctly less imagination than most constellations.
DAZZLING DIVERSITY
If coral reefs are the rainforests of the sea, the Coral Triangle is the Amazon jungle. Reefs here are so diverse they’re stacked full of species – a single square metre holds a dazzling array of shapes, colours and forms. These range from a multiplicity of colourful fish to corals of every type, camouflaged crabs, eels, rays, turtles, sharks, dolphins and even crocodiles. And that’s just underwater.
It’s a place of superlatives – and the statistics really are impressive. It is home to 83 per cent of Indo-Pacific coral species, and single reefs here hold four times as many species as the entire Atlantic Ocean. While the Caribbean has only 61 coral species, the nations of the Coral Triangle all have reefs with more than 500. The epicentre of the whole thing is the Bird’s Head Peninsula of West Papua with a grand total of 574 species – 72 per cent of the world’s coral species on one headland.
The Bird’s Head and the adjacent islands of Raja Ampat are a Mecca for marine biologists and divers alike. While some love coral for coral’s sake – and the formations here are spectacular – the reef itself also provides a literal bedrock for a huge assortment of fish and other animals, including 2,228 fish species and six of the world’s seven marine turtle species. It also supports vast schools of oceanic fish in the surrounding waters.
In 2008 I dived with the biggest, most spectacular group of fish I’ve ever seen: a 5,000-strong school of 1.2m tuna, in the bright blue waters of Papua New Guinea’s Bismark Sea. That’s an incredible 150,000kg of fish in a single school (I know that weight is accurate as that’s what was landed on the industrial fishing boat that caught them all in a net).
The waters of the Coral Triangle face the same demands as our seas the world over, but they are naturally incredibly rich. They are a spawning and growth area for five tuna species, and collectively make up the largest tuna fisheries in the world, bringing vital income to the area. It’s the health and diversity of the coral life that underpins the health and diversity of this whole ecosystem.
Why is it so diverse? Theories include that the area is a hotbed of evolution, and a meeting place of Indian Ocean and Pacific species. According to the work of renowned coral taxonomist, Professor Charlie Veron, the truth is most likely a combination, but the biggest factor is the sheer number of
islands. The Triangle encompasses the largest archipelago in the world, complex and convoluted coastlines with deep water nearby provide a huge diversity of habitats, and corresponding niches for a huge diversity of species.
So the Triangle is a varied coral haven, but that doesn’t explain why reefs further away are less diverse. There are a few points of explanation here. The first is that corals do better in the tropics. They are in competition with seaweeds for space on the sea floor, and only when it’s warm enough can they grow fast enough to avoid being smothered by the weeds’ slippery fronds. So, reduced diversity is correlated with distance from the equator, and decreasing temperature.
That’s not the only story, though. What’s more surprising is the lateral trend. The further you get from the Coral Triangle the fewer coral species there are. So what’s going on? A big clue is that rather than having novel species of their own, distant Pacific reefs tend to have subsets of species found in the Triangle. That fact, along with eastward-flowing ocean currents, indicates that these species originally came from the Triangle area. While corals produce tiny larvae capable of crossing ocean basins in the plankton, those larvae are microscopic drifters and can’t swim against those easterly ocean currents. It’s a one- way trip with no return, and so these species are largely surviving settlers from the west.
Corals are important because they build habitats. Like high-rise cities under the sea, coral reefs house a far greater mass of fish and other animals than an ocean floor that is just plain rock. Coral is the ultimate of nature’s architects, and the intricate coral skeletons can, over time, create structures large enough to be visible from space. More vast and enduring than any human city, many reefs have grown up over millions of years.
Providing biologically fabricated habitats for marine life, from crabs and urchins to fish and everything inbetween, each coral species has its own unique skeletal structure. A diversity of coral forms provides the diversity of homes needed by marine species. In fact, a quarter of all life in the oceans is dependent on coral reefs for at least one stage of its life cycle. So take away the reefs and you take away their habitat; they cannot survive.
TWIN THREATS
It has been estimated that we have lost 50 per cent of the world’s coral reefs in the last 30 years, and scientists predict that by 2050 we may have lost most reefs as we know them. The big problems are coral bleaching and ocean acidification, with both ultimately linked to anthropogenic (human-induced) high CO2 levels in Earth’s atmosphere. Often said to be the equivalent of the ‘canary in the coalmine’ when it comes to climate change, corals are extremely sensitive to increasing sea temperatures.
‘Bleaching’ is a coral’s stress response to a number of causes but the biggest events are due to temperature. Just 1–2°C above the normal local limit the coral’s usually beneficial internal algae can begin photosynthesising at such a high rate that the amount of oxygen they produce becomes toxic and the coral expels the algae. Since a coral’s colour is provided by its algae, their loss causes it to ‘bleach’ pale or bright white as its skeleton becomes visible through its tissues. If high water temperatures persist, or the corals aren’t able to establish new populations, they die, becoming overgrown by seaweed, and flattened by ocean currents.
The biggest bleaching episodes are often linked to El Niño events, which cause warmer than usual seawater to pool in the western Pacific. Massive bleaching is currently underway off Australia, with two-thirds of the Great
Barrier Reef suffering. Yet ocean acidification is even more insidious. High CO2 levels in the atmosphere cause more to dissolve into the water at the ocean’s surface. This is a problem for corals, as the more acidic the water, the harder it is for them to extract calcium carbonate to build skeletons.
Because of the way ocean water circulates, it has been predicted that the effects of CO2 already absorbed into the oceans will only start to be seen in corals in the next 20 to 30 years. This means that rising CO2 levels now are building up even more trouble for the future. In 2016 we exceeded 400ppm (parts per million) of CO2 in the Earth’s atmosphere, a startling rise from 328ppm in 1979. Scientific models show that levels of 387ppm cause a steady decline in coral reefs over time, and at 450ppm this decline becomes rapid, with an accompanying loss of diversity.
The historic Paris Agreement of 2015 resulted in targets to limit the rise of CO2 as soon as possible, and keep the global temperature rise to well below 2°C above pre-Industrial Revolution temperatures. But recent studies question our ability to achieve even this. Meanwhile, scientists are also looking for practical things to do in the short term.
One new project, ‘50 Reefs’, aims to identify reefs that are doing well and protect them from localised stresses with the hope that their larvae can then re-seed reefs that have been killed. While many of the world’s coral reefs are already badly damaged, overall reefs are by no means beyond repair, and some are still healthy – including those of many Coral Triangle countries such as the Solomon Islands.
HANGING IN THE BALANCE…
So are Coral Triangle reefs a stronghold that can re-seed other reefs? Maybe, but there has been bleaching here before, and success relies on us keeping a lid on ocean temperatures so corals can settle and grow. It may be a ray of hope – but it’s not a solution. One thing is for sure: while some reefs are coping better than others, we can’t let temperatures get much higher and the threat of acidification still hangs over all reefs.
If coral reefs are the canary in the coal mine, then the reality is we should be using them as such. In mining terms, saving the canary meant saving everyone. With so much marine life and human food security dependent on coral reefs, it would be prudent for us to see them the same way. In the words of Professor Ove Hoegh-Guldberg: “You can’t destroy a whole habitat and expect to still have the animals that call it home.”