Saturday, August 28, 2010
The rising acidity of the world's oceans – one of the key fears for the world's seas in the 21st century – is likely to have been responsible for massive species extinction in the past, scientists have found.
Researchers from the University of Plymouth and the University of Santa Catarina, Brazil, studied single-celled organisms called foraminifera, or "foram" around volcanic carbon dioxide vents off the island of Ischia, near Naples in Italy.
The study, published in the September issue of the Journal of the Geological Society, found that increasing CO2 levels – raising the acidity of the water to a lower pH value – caused foram diversity in the "natural laboratory" to fall from 24 species to only four.
"Previous studies have shown a reduction in diversity of 30 per cent, but this is even bigger for forams," said Dr Jason Hall-Spencer, one of the study's co-authors.
"A tipping point occurs at mean pH 7.8. This is the pH level predicted for the end of this century."
Rising carbon dioxide levels acidify the ocean, which has a particularly devastating effect on organisms that have calcium carbonate shells, like foraminifera.
"Forams are well preserved in the fossil record, which is why we chose to study them," said Dr Hall-Spencer.
"We knew the results were likely to show a decline in foram diversity but we weren't expecting such a seismic shift."
Forams record past events in the geological record – in particular, the effect of the Palaeocene-Eocene Thermal Maximum (PETM), a period of massive carbon release and rapid warming 55 million years ago, accompanied by extinctions in marine life. It is also thought to have seen a period of ocean acidification.
"That was a period when massive changes in marine ecology happened," Dr Hall-Spencer added.
Our natural laboratory provides a glimpse into the future of our oceans.
"These are the first CO2 vents to be used to study ocean acidification. They allow us to observe how ecosystems react to changes in ocean acidity.
"At a mean pH level of 7.8, calcified organisms begin to disappear, and non-calcifying ones take over. We are headed towards that being the case in this century.
"The big concern for me is that unless we curb carbon emissions we risk mass extinctions, degrading coastal waters and encouraging outbreaks of toxic jellyfish and algae."
Co-author Professor Malcolm Hart will be presenting the research to the 2010 Forams meeting in Bonn on Friday, September 6.
This weekend, Deborah Wall-Palmer will present the work being done by Plymouth on the last 250,000 years of ocean acidification at the International Palaeoceanography Conference in San Diego, which runs from August 29 to September 3.
http://www.thisisdevon.co.uk/news/Researchers-blame-sea-acidity-killing-species/article-2579103-detail/article.html
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