The longest lived coral colony on record is from a species of black coral from the genus Leiopathes that had an estimated age of 4,265 years old using radiocarbon dating methods – making it perhaps the oldest known living marine organism.
Researchers from Stanford University, Lawrence Livermore National Laboratory, and the University of California at Santa Cruz used radiocarbon dating to estimate age and growth rates of specimens of gold coral of Gerardia sp. and black coral of Leiopathes sp. collected off the coast of the Hawaiian Islands.[a] The longest-lived Gerardia sp. and Leiopathes sp. specimens were 2,742 years and 4,265 years, respectively. They estimated that the average radial growth rates of these specimens were as low as 4-35 micrometers per year. For scale, 50 micrometers is about the size of a dust speck and the diameter of a human hair is approximately 80 micrometers.
Some species of gold and black corals are harvested for jewelry. The extremely slow growth rates and longevity of the species estimated in this study put into question how renewable these resources are and whether sustainable commercial harvests are possible. In addition, corals may provide habitat for some commercially important fish species and are susceptible to damage caused by bottom-tending fishing gear. Recovery from such damage may take millennia.
Radiocarbon dating uses the fraction of the radioisotope 14C (radioactive isotope of carbon-14) to determine the age of any organic (carbon-based) material. When plants photosynthesize, they incorporate the same proportion of 14C that is in the atmosphere. When animals consume the plants, they incorporate that fraction of 14C, but the fraction of 14C decreases overtime at a fixed rate as the 14C decays (this rate is termed the half life). Comparing the fraction of 14C in organic material, such as dead tissue or skeletons, to what was expected to be in the atmosphere allows researchers to estimate age.
Results from radiocarbon dating remain contentious with some scientists. With regard to deep-sea corals, some question whether they feed on re-suspended sediments that may contain "old" 14C, and therefore skew the age estimates. However, results of this study indicated that the living polyps of these coral colonies had 14C signatures that were only a few years old, suggesting that they were consuming recently formed organic material that may be sinking from near the ocean surface, whereas the underlying skeletons were thousands of years old, making these colonies the oldest known living marine organisms. [a] Other recent studies have also found black and gold coral colonies in the Atlantic that appear to be over 1,000 years old.