Krill: the food that keeps Antarctica alive is under threat

Page - May 12, 2009
Antarctic krill are small shrimp-like crustaceans that are the principle food source for many Antarctic predators including seals, penguins, albatross, various fish species and the seven species of baleen whales that feed in the Southern Ocean.

Occurring in vast swarms, krill has long been targeted by fishing vessels from several nations. 

The advent of new technology that enables a single state-of-the-art trawler to vacuum up as much as 45,000 tonnes in a single season together with growing markets for aquaculture feed and nutritional supplements  are likely drivers for a massive expansion of the krill fishing industry in the near future. 

Even at current levels there are concerns that localized depletion of krill may be impacting on populations of krill predators.  Factor in the possible impacts of climate change and observed krill declines in some parts of the Southern Ocean and there is real reason to fear that the whole basis of the Antarctic food web is at risk.

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Occurring in dense concentrations, (there may be as many as 30,000 of the 6cm long animals in a single cubicmeter), estimates of the total weight of Antarctic krill range from 50-500 million metric tones, illustrating the huge uncertainties attached to all estimates of krill standing stock in the SouthernOcean. 

Although krill is arguably one of the best studied of marine animals, its ecology and population dynamics are not properly understood - especially what drives its abundance and distribution. (For more about the scientific uncertainties around Krill populations, see this technical paper: Gambling with Krill Fisheries in the Antarctic: large uncertainties equate with high risks.)

Enough is known about krill ecology and  population dynamics to suggest that climate change may have asubstantial effect on this keystone species and those that are dependent on it for food. For example, one serious potential impact of  reduced sea ice is failure of krill populations to reproduce and a subsequent failure to recruit into the population over a much wider area.

It has been known for some time that Antarctic krill feed on phytoplankton near the surface at night and sink deeper in the water column during the day to avoid predators, but recent research by some British scientists has revealed that they also parachute down several times during the night.  As a consequence ofthis behaviour, the krill is likely to be transporting more carbon from the surface layers to deeper waters than previously thought.  Lead author of the paper, Dr Geraint Tarling from the British Antarctic Survey estimates the annual sequestration of carbon by Antarctic krill may be the equivalent to the emissions of 35 million cars.

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