Krill are small, shrimp-like creatures that swarm in vast numbers and form a major part of the diets of whales, penguins, seabirds, seals and fish. But scientists say this key prey species in the Southern Ocean is retreating towards the Antarctic and this is all due to climate change(Amos, 2019).

If the shift is maintained, it will have negative ecosystem impacts, they warn. To add, there is some evidence that macaroni penguins and fur seals may be finding it difficult to get enough of krill to support their populations.

  

One of the krill competitors (Amos, 2019).

 Simeon Hill from the British Antarctic Survey  also mentioned BBC News that the results suggest that over the past 40 years, the amount of krill has, on average, gone down.  The location of the krill has contracted to much less of the habitat. That suggests all these other animals that eat krill will face much more intense competition with each other for this important food resource .The study was published in the journal Nature Climate Change (Amos, 2019).

The study was published in the journal Nature Climate Change. Its main focus was on the Scotia Sea and the Antarctic Peninsula, the places where the crustaceans are most abundant. Scientists have been gathering data in these areas since the 1920s. At first, krill were caught and recorded to understand the environmental consequences of commercial whaling, but the information has continued to be collected through to the present.

Dr Hill and colleagues say the change in the distribution and density of the crustaceans is a clear indication that emerges in the data from the late 1980s onwards. It coincides with a phase change in a climate oscillation known as the Southern Annular Mode or SAM. The SAM essentially describes the dominant pattern of pressure zones in the southern hemisphere outside of the tropics.The mode's switch in state in the late 80s produced warmer, cloudier, windier weather, and much less sea-ice in those areas where the krill had tended to congregate (Amos, 2019).

The larval stage of the crustaceans in particular has been strongly associated with the presence of a sea-ice habitat.

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The team's analysis indicates the centre of krill distribution has now moved to where more favourable conditions are found, tracking southward towards the Antarctic continent by about 440km, or four degrees of latitude. Even the average size of krill has lengthened over this period of time as well, this was said by Dr Hill.

Due to this, the population has increasingly become dominated by older and larger animals. This is a result of a decline in the number of krill entering the population - this is called juvenile recruitment.

  Research has shown that krill would shift southwards in the future, whereas the new research suggested this contraction was already under way (Amos, 2019).

The krill do not only support marine mammals and seabirds; an international fishery also extracts something on the order of a quarter of a million tonnes of the crustaceans each year in the Antarctic region.

The campaign group WWF-UK said the study showed the need to protect the waters off the Antarctic Peninsula with an effective network of marine protected areas - placing conservation above fishing interests (Amos, 2019).

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Jonathan Amos

BBC Science Correspondent, 2019, Antarctic krill: Key food source moves South. [Online]. Available:https://www.bbc.com/news/science-environment-46953652. Jan 21, 2019. Accessed: Jan 21, 2019.