IF CORALS could speak, what stories they would have to tell. It turns out that some giant deep-sea corals are more than 4000 years old, making them about the same age as the pyramids in Egypt.
The āgold coralā Gerardia and the black coral Leiopathes both grow several metres tall at depths of up to 500 metres on the Hawaiian seabed. They grow when each succeeding coral polyp secretes a thin layer of calcium carbonate onto the base of the ācupsā in which they live.
Previous studies had guessed their age at a few hundred years. Now , formerly at Stanford University in California, and colleagues argue that what they were counting as annual growth rings actually take much longer to form (Proceedings of the National Academy of Sciences, ).
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Using high-resolution radiocarbon dating, Roarkās team studied the coralsā outermost shell for traces of ābomb carbonā ā radioactive carbon produced during nuclear tests in the 1950s. They found it was present in only the upper 10 micrometres of the coral skeleton, suggesting this tiny slice took decades to build up.
Further carbon dating of layers down at the coralsā base revealed the oldest Gerardia to be about 2742 years old and the Leiopathes a whopping 4265 years old (see graph).
This has grave implications for the conservation of their ecosystem, says Roark. āBecause they are so big, they form the habitat for many other species,ā he says. If the corals die, thousands of years will go by before these speciesā habitats return.
Roark would like to see governments adopt measures to protect coral beds from deep-sea fishing, such as bans on trawling, and a permanent ban on using these species in the jewellery trade. āOn a human timescale, there is no way to sustainably harvest these animals,ā he says. āWe know next to nothing about how they spawn, settle and regenerate. I have seen very few younger and smaller colonies, so even slow regeneration might not be a very likely option.ā
He also hopes that preserving these coral species could be useful for us. āGiven their slow growth, we may be able to use them as high-resolution records of past climate change.ā
