June 9, 2008

Ocean Acidity Rises as Marine Life Decreases

A team of UK scientists has documented the affects of carbon dioxide on marine life.

By studying naturally occurring carbon dioxide vents in the sea floor, researchers believe they were able to gauge how CO2 will impact marine life.

Writing in the journal Nature, the scientists noted a declining number of species as well as snails with their shells disintegrating. They imply that these impacts could occur worldwide with the increasing levels of CO2 in the atmosphere.

The team investigated these impacts in the Mediterranean Sea near the Italian coast.

"It's clear that marine food webs as we know them are going to alter, and biodiversity will decrease," said Jason Hall-Spencer from the University of Plymouth, and the team's lead researcher.

"Those impacts are inevitable because acidification is inevitable - we've started it, and we can't stop it."

He also noted that seas have become more acidic since the industrial revolution, and even a sharp fall in emissions would not prevent further acidification.

Globally, the seas now have an average pH of about 8.1 - down about 0.1 since the dawn of the industrial age. Around the vents, it fell as low as 7.4 in some places. But even at 7.8 to 7.9, the number of species present was 30 percent down compared with neighboring areas.

The rise in ocean acidity affects marine life by slowly eliminating the concentration of calcium carbonate, which corals and other life forms use to construct their shells and external skeletons.

The scientists reported that coral was not present, and species of algae that rely on calcium carbonate were replaced by those that do not use it.

Snails were seen with their shells dissolving. There were no snails at all in zones with a pH of 7.4.

However, seagrasses, which benefit from added carbon, thrived in the region near the vents.

Elliott Norse said that these new findings give confirmation to those found in laboratory tests.

"I can't count the number of times that scientific talks end with 'responses have not yet been documented in the field'," said Elliott Norse, president of the Marine Conservation Biology Institute.

"This paper puts that to rest for several ecologically important marine groups."

Dr Hall-Spencer said the changes occurring around the Mediterranean Sea are likely to be seen around the world.

"I think we will see the same pattern in other parts of the world, because we're talking about keystone species such as mussels and limpets and barnacles being lost as pH drops," said Dr Hall-Spencer.

The IPCC suggests that some areas, notably the Southern Ocean, might feel the impacts at lower concentrations of CO2.

Last month, scientists reported that water with CO2 levels high enough to be "corrosive" to marine life was rising up off the western US coast.

"If [pH 7.8] is a universal 'tipping point', then it indicates that sections of the western coast waters off North America may have passed this threshold during periods when this upwelling of waters high in CO2 occurs," commented Carol Turley from Plymouth Marine Laboratory (PML), who was not involved in the Mediterranean Sea study.

Organisms are also harmed by rising temperatures, and studies are ongoing into the combined effect of a warming and acidifying ocean.

During the coming week, scientists will announce the inauguration of the European Project on Ocean Acidification (Epoca), a four-year initiative aiming to find some answers.

"The reason that the oceans are becoming more acidic is because of the CO2 emissions that we are producing from burning fossil fuels," said Dr Turley.

"Add CO2 to seawater and you get carbonic acid; it's simple chemistry, and therefore certain.

"This means that the only way of reducing the future impact of ocean acidification is the urgent, substantial reduction in CO2 emissions."


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VIDEO: Scientists study conditions at the bottom of the Mediterranean Sea


University of Plymouth