Rising acidity levels threaten ocean's food chain, study finds
The shells of some marine snails in the seas around Antarctica are dissolving as the water becomes more acidic, threatening the food chain, a study published in the journal Nature Geoscience said on Sunday.
The tiny snails, known as ‘‘sea butterflies’’, live in the seas around Antarctica and are left more vulnerable to predators and disease as a result of having thinner shells, scientists say.
The study presents rare evidence of living creatures suffering the results of ocean acidification caused by rising carbon dioxide levels from fossil fuel burning, the British Antarctic Survey said in a statement.
‘‘The finding supports predictions that the impact of ocean acidification on marine ecosystems and food webs may be significant.’’
The tiny snail, named for two wing-like appendices, does not necessarily die as a result of losing its shell, but it becomes an easier target for fish and bird predators, as well as infection.
This trend may have a follow-through effect on other parts of the food chain, of which they form a core element.
The world’s oceans absorb more than a quarter of man-made carbon dioxide emissions, which lower the sea water pH.
Since the beginning of the industrial era, our oceans have become 30 per cent more acidic, reaching an acidity peak not seen in at least 55 million years, scientists say.
Scientists discovered the effects of acidification on the sea butterflies from samples taken around the Scotia Sea region of the Southern Ocean in February 2008.
Oceans soak up about a quarter of the carbon dioxide released into the atmosphere each year and as CO2 levels in the atmosphere increase from burning fossil fuels, so do ocean levels, making seas more acidic.
Ocean acidification is one of the effects of climate change and threatens coral reefs, marine ecosystems and wildlife.
The study involved researchers from the British Antarctic Survey, Royal Netherlands Institute for Sea Research, the US National Oceanic and Atmospheric Administration (NOAA) and other institutions found.
"The corrosive properties of the water caused shells of live animals to be severely dissolved and this demonstrates how vulnerable pteropods are," said lead author Nina Bednarek, from the NOAA.
"Ocean acidification, resulting from the addition of human-induced carbon dioxide, contributed to this dissolution."
Until now, there has been little evidence of the impact of ocean acidification on such live organisms in their natural environment and the study supports predictions that acidification could have a significant effect on marine ecosystems.
The researchers examined surface water, where wind causes cold water to be pushed up from deeper water, because it is usually more corrosive to a particular type of calcium carbonate which the sea snails use to build and maintain their shells.
"We know that the seawater becomes more corrosive ... below a certain depth which occurs at around 1,000m. However, at one of our sampling sites, we discovered that this point was reached at 200m depth. Marine snails - pteropods - live in this top layer of the ocean," Bednarek said.
Climate models forecast more intense winds in the Southern Ocean this century if CO2 continues to increase, which will make the mixing of deep water with more acidic surface waters more frequent, the study said.
This will make calcium carbonate reach the upper surface layers of the Southern Ocean by 2050 in winter and by 2100 all year round, said the study's co-author Dorothee Bakker, research officer at the University of East Anglia.
If CO2 levels continue to rise in the future, surface waters could be almost 150 per cent more acidic by the end of this century, which has not been experienced for more than 20 million years.