WHALES, seals, penguins and albatrosses are under threat from a catastrophic decline of krill in the Southern Ocean, British scientists have found.

Research has disclosed that numbers of the tiny shrimp-like creatures that prop up the Antarctic marine food chain have fallen by 80 per cent since the 1970s, creating food shortages that are endangering larger animals and birds.

The decline appears to have been caused by the loss of sea-ice around the frozen continent, and that is believed to be an effect of global warming.

Sea ice is critical to the life cycle of krill, as the ice shelters their larvae from predators and is rich in the algae on which they feed. The ocean around the mountainous continuation of the Andes within the Antarctic Circle, known as the Antarctic Peninsula, is an important breeding ground for krill. It is warming at one of the fastest rates of any location on the planet, with a corresponding reduction in the extent of sea-ice around it.

The findings suggest that this climate change may be having an effect on the long-term prospects of Antarctica’s large marine mammals and birds by severely disrupting the food chain. Angus Atkinson of the British Antarctic Survey, who led the research, said: “This is the first time that we have understood the full scale of this decline. Krill feed on the algae found under the surface of the sea-ice, which acts as a kind of nursery.

“The Antarctic Peninsula has warmed by 2.5C in the last 50 years, with a striking decrease in sea-ice. We don’t fully understand how the loss of sea-ice here is connected to the warming, but we believe that it could be behind the decline in krill.”

The results, which are published today in the journal Nature, also have important implications for commercial fisheries, many of which are founded on fish that feed on krill. Antarctic tourism could also be affected by the species’ decline, as many visitors to the continent are drawn there by its spectacular wildlife.

“These changes among key species have profound implications for the Southern Ocean food web,” Dr Atkinson said. “Penguins, albatrosses, seals and whales have wide foraging ranges but are prone to krill shortage.”

While krill stocks have been falling, numbers of transparent, tube-like creatures called salps are increasing. This may also be a symptom of rising temperatures in the region, as salps can tolerate much warmer water than krill.

Antarctic krill, which have the scientific name Euphausia superba, are among the most important animals to the ecology of the Southern Ocean. They are shrimp-like crustaceans that can grow to a length of 6cm (2.4in) and live for up to six years. They form the principal diet of many of Antarctica’s large mammals, birds and fish.

Previous studies have also indicated that numbers are in decline, but those was based on localised surveys that covered shorter periods of time than the new research.

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