Ancient reef may thrive again

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The remains of an extensive coral reef that flourished 9000 years ago have been discovered in the Tasman Sea in the South Pacific.

The ancient reef, known as a relict reef, was detected at a depth of 25–50 metres by a team of scientists from Australia and New Zealand.

The reef lies 600 km east of the Australian mainland and surrounds Lord Howe Island, which is currently fringed by a smaller living reef that is the southernmost coral reef in the world.

At this latitude (31° S), sea surface temperatures are at the lower limit for warm-water coral growth. However, the research team headed by Colin Woodroffe from the University of Wollongong believe that, later this century, increasing sea temperatures could allow the relict reef to become a substrate for new coral growth.

The researchers used radiocarbon and uranium-series dating to show that the corals from the ancient barrier reef were alive around 7000–9000 years ago, in the early Holocene period. The findings published in the journal Geophysical Research Letters also reveal that the relict reef is 20 times larger than the modern reef and covers an area of at least 145 km2.

The immense relict reef is believed to have died thousands of years ago due to flooding caused by rising sea levels. During the last 3000 years, corals have become re-established in a few localised areas of the relict reef, indicating that recolonisation is a possibility if environmental conditions become more favourable.

Reefs are currently threatened by global warming, and rising sea temperatures may begin to affect the geographical limits of coral growth. Although coral reefs in the hotter tropical latitudes of the world are at increased risk of bleaching, warmer seas may allow for reef expansion at the current southern, and northern, limits of colonisation.

For more information see the article: Woodroffe CD, Brooke BP, Linklater M, Kennedy DM, Jones BG, Buchanan C, Mleczko R, Hua Q and Zhao J-x (2010) Response of coral reefs to climate change: Expansion and demise of the southernmost Pacific coral reef. Geophys. Res. Lett. 37, doi:10.1029/2010GL044067