Coral reefs under siege from acidic oceans

Ocean acidification, a potentially disastrous consequence of global warming, is threatening the early life cycle of coral reefs near Florida and throughout the Caribbean, according to a new study published Monday.

While other research has looked at how the world's increasingly acidic oceans affect adult coral, this is the first one to document its impact on coral's early life stages.

Coral reefs don't just make pretty screen savers — they provide $30 billion of economic benefit to the USA each year through tourism, diving, coastal protection, commercial fishing and fishing communities, according to study lead author Rebecca Albright of the University of Miami's Rosenstiel School of Marine and Atmospheric Science.

Globally, she cites a 2003 study that found the coral reef industry is valued at $375 billion annually.

"There have been very few, if any studies that had looked at the effects on early life-history stages, such as fertilization, larval settlement and recruitment," Albright says. "Recruitment" refers to the process of replacing dead coral with new coral.

Over the next century, the study found that recruitment of new corals could drop by as much as 73%. The study appears in this week's issue of the Proceedings of the National Academy of Sciences.

"Reproductive failure of young coral species is an increasing concern since reefs are already highly stressed from bleaching (due to unusually warm sea water), hurricanes, disease and poor water quality," said Chris Langdon associate professor at the Rosenstiel School and co-author of the study.

Scientists in this study looked at one species of coral — Elkhorn coral, known as acropora palmata— a prime reef-building species that once dominated tropical coral reef ecosystems. Elkhorn was placed on the U.S. Endangered Species List in 2006 due in part to severe population declines over the past several decades.

"In order for that species to not go extinct, we have to be replacing them as we're losing them," says Albright. "The implications of this work show that ocean acidification … is interfering with that ability of the corals to be replaced."

Ocean acidification refers to the increased amounts of atmospheric carbon dioxide (caused by the burning of fossil fuels) absorbed into the world's oceans. This additional carbon not only warms the oceans, but also radically transforms their chemistry, according to a National Research Council report earlier this year.

When the ocean absorbs CO2 it depletes the water of carbonate ions by combining with CO2 to make carbonic acid. With the smaller amount of carbonate ions and increased acid, the ocean acidifies, pH lowers. Because coral reefs are made of calcium carbonate, they are now deprived of this ion to rebuild and grow.

Albright says the field of ocean acidification research has really only blossomed in the past 10 years, and it's only in the past couple of years that scientists have shifted their focus to look at the early life cycle in addition to the adults of various species, such as coral and shellfish.

"We're affecting the chemistry of the oceans at an unprecedented rate," she says. "It's a rate that hasn't been known to occur naturally for the last 60 million years."

Source:
USA Today, "Coral reefs under siege from acidic oceans", accessed November 9, 2010

Ancient coral reef uncovered in South Pacific

An ancient reef found in the Pacific may provide clues to what will happen to coral when sea temperatures rise. A team of researchers from Australia and New Zealand have discovered a huge 9,000-year-old reef surprisingly far south.

Lord Howe Island is 600km east of the Australian mainland and has a small modern coral reef - the furthest south in the world.

The ancient reef however is nearly 30 times as large as the modern reef.

The scientists, headed by Colin Woodroffe from the University of Wollongong in Australia and researchers from Geoscience Australia, discovered a large ridge about 30m under water in the Tasman Sea. (In lower right corner of map)

They have published their work in Geophysical Research Letters.

The team suspected it might be an ancient reef. The size and shape of the ridge can be mapped using a type of sonar called multi-beam echo sounding. The researchers could not be sure it was coral until they had taken samples.

Drilling for samples in the Tasman Sea is very dependent on weather and the seas can be rough - it involves lowering a submersible drill from a boat.

The samples confirmed that it was indeed coral and radiocarbon dating confirmed its age.

Other similar ancient reefs - called relict reefs - have been discovered before, but none as far south as this.

The team think that this reef died when it was flooded as a result of sea levels rising about 7,000 years ago, but the modern temperature at these latitudes also limits coral growth, which is why the relict reef is so much bigger than the modern reef.

Now that sea temperatures are rising, however, reefs may start to grow bigger at higher latitudes.

The relict reef doesn't have an extensive modern reef attached to it but it does have some individual corals which are newer - from the last 2,000 years.

This suggests that there is a suitable habitat for corals which might grow into a larger reef when temperatures rise further.

In the Northern Hemisphere both Florida and Bermuda have small reefs, though they are at the northern limits for warm-water coral life.

It is possible that large relict reefs might also be found in those northern waters. Like the Tasman Sea relict reef, these might be able to support new growth.

Rising sea temperatures are dangerous for coral reefs at hotter tropical latitudes but they may mean we see new reef growth at the far southern, and northern, limits of current reefs.

Source:
BBC News, "Ancient coral reef uncovered in South Pacific", accessed September 10, 2010