Oldest colonial organism

A study published in the PNAS journal on 31 March 2009 described a specimen of deep-sea Hawaiian black coral (Leiopathes annosa), found at depths of 300-500 m (985-1,640 ft) throughout the Hawaiian archipelago, USA, that was radiocarbon-dated to be 4,265 years old. This makes it not only the oldest-known skeletal-accreting marine organism, but also the oldest-known colonial animal (i.e., an association of conspecific animals in which the individuals are physically connected). This age refers to the collective skeleton produced by many generations of coral polyps, as opposed to individuals within the colony, which on average only live for around 2-5 years.

In the same study, another deep-sea coral - Gerardia, aka gold coral - was aged to be 2,742 years old, showing that Leiopathes is not alone in its extreme longevity. It was already known that these corals could live for many centuries, but not to this extent; previous to this study, another colony of Gerardia in the Pacific Ocean had been aged similarly at 2,740 ± 15 years; but the previous oldest known Leiopathes specimen (also from off Hawaii) had a 14C-estimated life span of "just" 2,320 ± 20 years.

Coral skeletons can be aged in a similar way to how trees are aged by studying their growth rings. A key factor behind these corals' long lifespan is their extremely slow development: radial growth rates for black and gold corals were calculated to be as low as 4 to 35 μm per year. The Hawaiian black coral is not quite as old as the oldest-known individual terrestrial trees: bristlecone pines of (Pinus longaeva) of California's White Mountains have been dated to exceed 5,000 years old. Clonal plants are likely even older still: a creosote bush (Larrea tridentata) found in 1980 in the desert near Palm Springs, California, USA was dated to be 11,700 years old.

In terms of other marine organisms, even older specimens of sponge have been found, such as glass sponges (class Hexactinellida) dating back as old as 11,000 years for a specimen of Monorhaphis chuni collected in the East China Sea. However, sponges (Porifora) are generally considered a primitive form of multicellular organism, rather than individual animals living in a colony.