A massive and ancient antipatharian colony at a seamount in the northwest Pacific

Many colonial anthozoans are ecosystem engineers and contribute to creating intricate benthic communities that often harbor high levels of marine biodiversity. Here, we report on an extraordinarily large antipatharian colony observed on the West Mariana Ridge in the Northwest Pacific. Based on colony form, morphological analyses, and DNA barcoding results, we identified the colony as Leiopathes cf. annosa . From in situ observations, we estimate the size of the colony as approximately 308 cm in height and 441 cm in width, with a central stem of 28 cm in diameter. If growth rates of Leiopathes species in this region of the Pacific Ocean are similar to those previously reported from Hawaii, this colony may be approximately 7000 years old, placing it among the longest-lived marine organisms reported. Seamounts in this region and such large anthozoan colonies should be targeted for more biodiversity investigation and future conservation.