Extinction .in

Ocean Acidification destroying Antarctic marine life

 
The research took place in the Southern Ocean
 

Marine snails in seas around Antarctica are being

affected by ocean acidification, scientists have found.

An international team of researchers found that the snails' shells are being

corroded.

Experts says the findings are significant for predicting the future impact of

ocean acidification on marine life.

The results of the study are published in the journal Nature Geoscience.

The marine snails, called "pteropods", are an important link in the oceanic

food chain as well as a good indicator of ecosystem health.
 

"They are a major grazer of phytoplankton and... a key

prey item of a number of higher predators - larger plankton, fish, seabirds,

whales," said Dr Geraint Tarling, Head of Ocean Ecosystems at the British

Antarctic Survey (BAS) and co-author of the report.

The study was a combined project involving researchers from the BAS, the

National Oceanic and Atmospheric Administration (NOAA), the US Woods Hole

Oceanographic Institution and the University of East Anglia's school of

Environmental Sciences.

Ocean acidification is a result of burning fossil fuels: some of the

additional carbon dioxide in the atmosphere is absorbed into oceans.

This process alters the chemistry of the water, making it more acidic.

 
Pteropods are an important food source for fish and birds
During a research cruise in the Southern Ocean in 2008, scientists assessed

the corrosive effects of upwelled water on pteropod shells.

Upwelling occurs when winds push cold layers of deeper seawater from around

1,000m towards the surface layers.

Seawater from these depths is more corrosive to aragonite, the type of

calcium carbonate that forms pteropod shells. The point at which this occurs is

known as the "saturation horizon".

"Carbonates in shells dissolve more when temperatures are cold and pressure

is high, which are the characteristic properties of the deep ocean," Dr Tarling

explained.

Scientists found that the combined effect of increased ocean acidity and

natural upwelling meant that in some areas of the Southern Ocean the saturation

horizon was around just 200m - the upper layer of the ocean where pteropods

live.

Dr Tarling explained the significance of these findings: "The snails do not

necessarily die as a result of their shells dissolving, however it may increase

their vulnerability to predation and infection, consequently having an impact to

other parts of the food web."

He said that although upwelling sites are a natural phenomenon in the

Southern Ocean, "instances where they bring the saturation horizon above 200m

will become more frequent as ocean acidification intensifies in the coming

years".

 
A pteropod (Limacina helicina antarctica) showing acute levels of shell dissolution
Interpreting the results

Dr Tarling said the study is "very much... a pilot study" and that it has

provided an important body of work regarding "how pteropods will respond to

future oceanic conditions".

To date there have been a number of laboratory studies predicting the effects

of ocean acidification on marine organisms, but none assessing the impacts on

live specimens in their natural environment.

"It took us several years even to develop a technique sensitive enough to

look at the exterior of the shells under high-power scanning electron

microscopes, since the shells are very thin and the dissolution pattern,

subtle," commented Dr Tarling.

He went on: "We are now undertaking a much more comprehensive programme

completely focussed on the effects of ocean acidification, not just on pteropods

but to a wider range of organisms."