Wednesday 3 January 2018

Porites australiensis: An exceptionally large Coral microatoll from Okinawa, Japan.

Stony Corals of the genus Porites are found on Reefs around the world, where they form large flat topped microatolls, rising above the surface of the reef. They are often used  by palaeoclimatologists to study ancient climates, since they tend to preserve oxygen isotope levels in the same proportion as the water they lived in, a proxy for the temperature of the sea. Due to this fossil Porites colonies have been widely sought out, and some remarkable specimens found, with the current largest known specimen coming from China and measuring about 9 m across.

In a paper published in the journal Coral Reefs on 3 October 2017, Ichiro Takeuchi of the Graduate School of Agriculture at Ehime University, and Hideyuki Yamashiro of the Tropical Biosphere Research Center of the University of the Ryukyus, describe the discovery of an exceptionally large Porites microatoll from the Okinawa Islands of Japan.

The colony was found about 150 m off the south coast of the island of Sesoko (which is itself about 500 m off the west coast of Okinawa Island) during an aerial drone survey of the area in March-April 2017. The atoll stands in water which is about 1.2-3.0 m deep at low tide, with a tidal range of about 2.3 m. The colony is a specimen of Porites australiensis 11.1 m across, making it the largest recorded Porites colony known, living or fossil, which given an estimated growth rate of 2.6–10.8 mm per year, makes the colony between 500 and 2100 years old.

Large Porites microatoll at Sesoko Island, Okinawa, Japan. Aerial photo taken from an altitude of 11 m at near low tide. The top of the microatoll is near the sea surface. Takeuch & Yamashiro (2017).

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