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Marine life 'has warming defences'

AMOS AIKMAN, April 09, 2012

MARINE life may be more tolerant of climate change than previously thought, with new research showing the world's most important calcifying organism can adapt to ocean acidification

In a study published in the journal Nature Geoscience today, German scientists found the key micro-organism, a species of coccolithophore important in burying carbon in rocks, evolved a tolerance to higher carbon-dioxide levels over multiple generations, whereas previous studies had tended to look only at a single generation.

Under normal conditions, the oceans absorb large amounts of carbon dioxide. Tiny organisms living in surface waters use carbon, oxygen and calcium to build their skeletons through a process known as calcification. When they die, those skeletons and other debris sink to the bottom of the ocean where they are buried.

When the ocean is rich in nutrients, those micro-organisms can become so abundant that their "blooms" are visible from space as milky trails in the water. Thus, large amounts of carbon are removed from circulation.

However, when CO2 levels get too high, seawater acidity increases, making it harder for the organisms to grow. Scientists have long feared man-made carbon emissions will disrupt this natural balance beyond repair.

In the past, most studies of coccolithophores have focused on short timespans covering just a few generations. None tested for evolutionary adaptation.

However, in this latest study, the scientists deliberately bred coccolithophores to increase their tolerance to CO2, mimicking what is presumed would happen in nature over longer timescales. "Compared with populations kept at ambient CO2 partial pressure, those selected at increased partial pressure exhibited higher growth rates when tested under ocean acidification conditions," the authors wrote.

"Calcification was partly restored: rates were lower under increased CO2 conditions in all cultures, but were up to 50 per cent higher in adapted compared with non-adapted cultures."

The authors argue the findings, if upheld in nature, show evolution may help these and other tiny organisms that form the base of the marine food chain adapt to climate change better than previously thought.

The findings come after several other recent studies that showed corals - another species of calcifying organism - could adapt to ocean warming better than previously thought.