Deep-sea corals are the oldest living animals with a skeleton in the seas, say scientists who claim to have found a 4,265-year-old coral species off the coast of Hawaii.

Deep-sea corals grow on underwater mountains and continental margins at depths of about 1,000-10,000ft (300-3,000m). They are as threatened by climate change and pollution as shallow water corals.

A coral ‘head’, commonly perceived to be a single organism, is formed from thousands of individual but genetically identical polyps, each polyp only a few millimeters in diameter. Over thousands of generations, the polyps lay down a skeleton that is characteristic of their species.

Samples of two species examined in the study, gold coral (Gerardia sp) and deep-water black coral (Leiopathes sp), were gathered from off the coast of Hawaii with submersibles.

Previous estimates of the corals’ ages, made by counting what were thought to be annual growth rings, put the maximum age for Gerardia sp in Hawaii at about 70 years.

But radiocarbon studies had pinned ages of about 2,000 to 3,000 years on other Gerardia colonies in the Atlantic and Pacific. Similar dates were found for some Leiopathes specimens.

Brendan Roark of Texas A&M University in College Station, Texas, and his colleagues made radiocarbon measurements of the skeletons of the Hawaiian specimens and came up with similarly ancient ages: about 2,742 years for Gerardia and 4,265 years for Leiopathes.

‘These results show that Leiopathes is the oldest skeletal-accreting marine organism known and, to the best of our knowledge, the oldest colonial organism yet found,’ the study authors wrote. Their findings are detailed in the March 23 issue of the journalProceedings of the National Academy of Sciences.

The ages imply that the corals’ skeletons grow much more slowly than previously thought, only a few micrometers a year (one micrometer is about the diameter of a human blood cell). The tiny coral polyps that live inside the skeletons are only a few years old, meaning they are continually replaced for centuries to millennia while the supporting skeleton builds up around them.

The authors noted that Hawaiian deep-sea corals, which support diverse fish and invertebrate communities, are under threats from bottom trawling, which damages the coral beds, harvesting for jewelry and other activities associated with commercial fishing.

Warming ocean waters and ocean acidification (the result of water absorbing the carbon dioxide accumulating in our atmosphere) can also impact coral survival. A 2008 study estimated that the increasing acidity of the ocean could wipe out most corals in the ocean by 2050. These conditions could also make corals more susceptible to diseases .

If the corals disappear, the communities they support could go as well. Caribbean reef fish populations have suffered major losses in the last 15 years, according to a study in the March 19 issue of the journal Current Biology.

Roark and his fellow researchers for the study say that the slow growth rates implied by their study make coral conservation even more critical, since the colonies are slow to replace what is lost.

Corals play host to many other marine organisms, and are hotspots of ocean biodiversity . The largest coral reef system in the world is the Great Barrier Reef off the coast of Queensland, Australia. Big reefs are also found in the Red Sea, along the coast of Mexico and Belize, the Bahamas and the Maldives.