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