Antarctic whales, seals and penguins could be threatened by food shortages in the Southern Ocean. Numbers of Antarctic krill (Euphausia superba), a shrimp-like crustacean at the heart of the food chain, are declining. The most likely explanation is a dramatic decline in sea-ice. The results are published this week in the journal Nature.
Sea-ice is a vital feeding ground for the huge number of krill in the Southern Ocean. The new research shows that krill numbers have dropped by about 80% since the 1970's. Less sea-ice during the winter is likely to be the cause and may explain declines seen in several species of penguins.
Lead author Dr Angus Atkinson from British Antarctic Survey, says: "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, a key breeding ground for the krill, has warmed by 2.5°C 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 implications are commercial as well as scientific, as the Southern Ocean is a valuable resource for fisheries. Thousands of tourists are also attracted to Antarctica to enjoy the spectacular wildlife, most of which feed on krill. By knowing how the environment affects this unique food web, we can predict how it will respond to future change.
Long-term decline in Antarctic krill stock and increase in salps within the Southern Ocean by Angus Atkinson, Volker Siegel, Evgeny Pakhomov and Peter Rothery was published in Nature on 4 November 2004.
Antarctic krill (Euphausia superba) are one of the most important animals in the Southern Ocean. These shrimp like crustaceans grows up to a length of 6cm and can live for 5-6 years. Krill feed on phytoplankton and are in turn eaten by a wide range of animals including fish, penguins, seals and whales. They are also a potentially valuable source of protein for man and can be fished easily with large nets.
There was previous speculation that krill stocks might have declined - this was based on localised surveys spanning a shorter duration than the current study. Four years ago BAS started an international collaborative project to widen the time- and space-scales of sample coverage. Nine of the countries working in Antarctica pooled their data spanning 40 Antarctic summers, over the period 1926 to 2003. They allow for the first time a large-scale view of change across the Southern Ocean.
Air temperatures in the Antarctic Peninsula region have risen by over 2.5°C in the last 50 years, about 5 times faster than the global mean rate.
Despite the decline of krill some species may have benefited from environmental change. A jelly-like animal known as salps have increased.
Early last century, man's over-exploitation of whales preceded a rapid increase in krill predators such as fur seals. Following this shift in the predator balance, a return of the whales to pre-exploitation levels now faces the further problem of lower krill density.
This research is part of the BAS DYNAMOE Programme (Dynamics and Management of Ocean Ecosystems) - see: http://www.antarctica.ac.uk/Science/Programmes/
British Antarctic Survey is a world leader in research into global issues in an Antarctic context. It is the UK's national operator and is a component of the Natural Environment Research Council. It has an annual budget of around £40 million, runs nine research programmes and operates five research stations, two Royal Research Ships and five aircraft in and around Antarctica. More information about the work of the Survey can be found at: http://www.antarctica.ac.uk
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