Almost half of Antarctic krill offspring would struggle to survive in vast regions of the Southern Ocean's increasingly acidic waters by the end of the century if carbon emissions continue unchecked, climate study projections show.
If such conditions continued, researchers at the Australian Antarctic Division predict krill populations could be wiped out by 2300.
Marine biologist Rob King said krill were the main food source of whales, seals and penguins in the Southern Ocean.
But as carbon dioxide levels in the atmosphere have increased over the past 250 years, so has the amount of the gas absorbed by the oceans, making them more acidic and less hospitable for aquatic life.
''Up to a third of all carbon dioxide that humans produce each year dissolves into the sea,'' he said. But dramatic population declines could be avoided if emissions were sharply reduced, the study found.
The research team led by So Kawaguchi measured the level of carbon dioxide in seawater that krill eggs could tolerate.
Their experiments in the Antarctic division's krill aquarium found the number of eggs hatching started to decline when the level of carbon dioxide reached 1250 microatmospheres.
At 1500 microatmospheres, hatch rates were 30 per cent lower than in seawater containing 1000, a level the eggs could accommodate. Almost no embryos hatched at 1750 and 2000 microatmospheres. Present levels of carbon dioxide below the surface of the Southern Ocean vary, but average about 500 microatmospheres.
Dr Kawaguchi said the fate of krill was closely linked to the entire Antarctic ecosystem.
''A substantial decline in krill numbers would have disastrous implications not only for the health of the ocean environment but also on the future survival of the mammals and sea birds that rely on them,'' he said.
Study findings were published in the journal Nature Climate Change.