Extreme longevity in proteinaceous deep-sea corals
The "gold coral" Gerardia and the black coral Leiopathes both grow several meters tall at depths of up to 500 meters on the Hawaiian seabed. They grow when each succeeding coral polyp secretes a thin layer of calcium carbonate onto the base of the "cups" in which they live.
Previous studies had guessed their age at a few hundred years but the PNAS study by Brendan Roark and colleagues argues that what were previously counted as annual growth rings actually take much longer to form. Using high-resolution radiocarbon dating, Roark's team studied the corals' outermost shell for traces of "bomb carbon" - 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 corals' base revealed the oldest Gerardia to be about 2742 years old and the Leiopathes 4265 years old.