From: Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research
Published June 6, 2017 09:43 AM

Why do Antarctic krill stocks fluctuate?

It is only six centimetres long, but it plays a major role in the Antarctic ecosystem: the small crustacean Euphausia superba (Antarctic krill). It's one of the world's most abundant species and the central diet of a number of animals in the Southern Ocean. For a long time, scientists have been puzzled why the size of krill stocks fluctuates so widely. In a new study headed by Prof. Bernd Blasius and Prof. Bettina Meyer, a group of scientists from the University of Oldenburg's Institute for Chemistry and Biology of the Marine Environment (ICBM) and the Bremerhaven-based Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) have shown that the competition for food within the population is responsible for the variability.

The researchers evaluated long-term data and developed a mathematical model to investigate the change in the krill stocks. Their findings have now been published in the latest issue of the respected journal Nature Ecology & Evolution.

It has long been known that stocks of Antarctic krill vary widely over a five to six-year period, with more than ten-fold changes in the biomass. To date, experts have presumed that climatic factors, characterised by distinct seasons, were responsible for this “krill cycle”. But there was never any real proof of this assumption. Now, analyses by the researchers from Oldenburg and Bremerhaven indicate that it is a self-generating mechanism, induced within the population, that is responsible for the cycle. Particularly in the Antarctic autumn, the small crustaceans within a swarm increasingly compete for food. At this time of year the larvae and adults need to lay down sufficient fat reserves for the upcoming winter. At the same time the krill’s food supply – microscopic small algae, the phytoplankton – becomes less abundant when the days become shorter. Large krill stocks have to starve for long periods, have to overwinter and reproduce. All these factors cause the fluctuation of a population.

Read more at Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research

Photo credit: Uwe Kils via Wikimedia Commons

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