Most people don’t realise that large pieces of coral, which have been painted brown and attached to the skull by common wood screws, can make a child look like a deer. Jack Handey, US comic
Corals share their closest family ties with jellyfish. It’s hard to imagine two more different-looking animals, but they are both members of the Cnidaria phylum (from knide, Greek for stinging nettle). Coral looks far more like a colourful, baroque relative of the seaweeds, but close examination reveals it as an animal, or rather a host of animals, as each frond is composed of thousands of tiny individual “polyps”, rather like miniature sea anemones. Each polyp has a fringe of stinging tentacles, a bottom-cum-mouth and stomach, just like their cousins. But they do something that the others don’t: they build reefs, the rainforests of the ocean.
By sucking in seawater, polyps extract the elements they need to lay down a solid base of calcium carbonate. This base is added to gradually, at about an inch a year. This provides a cup-like shelter for each polyp to hide in and keeps them moving upwards towards the light. Coral polyps “grow” rock, in the same way we grow bones. Eventually, as millennia pass, a reef forms. If you gathered all the coral reefs in the world together they would cover an area twice the size of the UK.
With friends like these, who needs anemones?
The myriad colours of the coral reef aren’t of the coral’s doing. Coral has evolved one of the most mutually beneficial partnerships on the planet, with tiny algae called dinoflagellates (Greek for “whirling whips”, which describes their method of propulsion), small enough to live, two million to the square inch, in the reef’s surface. The coral polyps catch microscopic organisms with their tentacles, and the waste products (mostly carbon dioxide) feed the on-board algae. In return, the algae give the polyps their striking colours, and produce most of their energy by photosynthesising sunlight.
This is why you find most corals in shallow, clean, sunlit water. The algae even make a sunscreen that protects the polyps, allowing them to keep working all day. And it is hard work: mutatis mutandis, reef-building corals use up two-and-a-half times more energy than a resting human.
Coral’s relationship with algae is not without its tensions. If the algae can get food more easily elsewhere, as happens when the reef silts up, or becomes too warm or polluted, they will leave, “bleaching” the polyps white, and condemning them to death. In the record-breaking heat of 1997 and 1998, a sixth of the world’s coral reefs “bleached”. It is now estimated that a tenth of all the world’s reefs are dead, and if the carbon levels in the oceans continue to rise, the rest may follow by 2030.
Coral reefs are on the front line in the war against global warming. However, it is encouraging to note from the fossil record that corals have almost gone extinct five times before, but have always managed to fight their way back.
Coral doesn’t age like we do: most of its cells are the equivalent to stem cells in a developing human embryo, allowing even a small fragment to regenerate into a whole polyp. Some polyps may be over a century old.
Indirectly, coral helped Darwin refine his ideas about evolution. Although he had no idea about the symbiotic relationship with algae, his first scientific book after returning from the voyage on the Beagle was an account of the formation of coral reefs in 1842. He theorised (correctly) that atolls were formed by undersea volcanoes slowly sinking under the surface of the ocean, leaving a ring of coral still growing upwards towards the light. The long process of geological change this implied confirmed his hunch that constant change was at work all over the biological kingdom.
Buried at sea
After you die, you could be turned into a coral reef (by a company called Eternal Reefs). Your ashes will be combined with concrete, sunk to the bottom of the ocean and will form an artificial reef to attract corals, sponges, algae and barnacles.
The people of Palau, an island in the South Pacific, squeeze sea cucumbers until they expel their sticky guts, which they use to protect their feet when they walk on the reef. Dolphins attach bits of sponge to their snouts as safety masks when hunting among sharp coral.
'The Secret Museum' by Molly Oldfield (HarperCollins, RRP £25) is available from Telegraph Books (0844 871 1515) at £23 plus p&p.
Next week: QI’s rave from the conclave