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Explanations

Ecosystems under stress: Is the blue whale's food chain under threat?

Andy Day

24th April 2017

It's the largest animal on the planet, but the blue whale's food involves hundreds of thousands of shrimp-like krill. While the southern ocean is full of these crustaceans, their winter food source of algae is under threat as warmer ocean temperatures melt the sea-ice on which they cling. Is the future starting to flash red for the blue whale?

This remarkable drone footage from National Geographic shows a blue whale scooping up a vast swarm of krill off the coast of New Zealand. There has been a substantial decline in krill in the last 40 years for, as yet, indeterminate reasons. It may be due to the growth of whale populations as their numbers recover from decades of commercial whaling. Or - it may be due to climate change and ocean acidification. Krill grow fastest in cold waters with low acidity. In the lean months of winter they feed off the algae that occupies the nooks and cavities on the underside of sea-ice around the Antarctic perimeter. There are concerns that as ocean waters warm, ocean acidification occurs as the sea absorbs more CO2 in the ocean-atmosphere exchange, and as sea-ice melts faster depleting the algae store, then krill are hit by a triple whammy. Blue whale numbers are recovering from close to extinction in the 1950s. Whether the recovery will continue, or whether they will find the ocean ecosystem starts to become a tougher environment, remains to be seen. But understanding the complex interactions in the marine ecosystem and its interplay with climate change processes is fundamental in planning for their long-term survival.

Read more about the decline of krill in this article by the Climate News Network


Andy Day

Andy recently finished being a classroom geographer after 35 years at two schools in East Yorkshire as head of geography, head of the humanities faculty and director of the humanities specialism. He has written extensively about teaching and geography - with articles in the TES, Geography GCSE Wideworld and Teaching Geography.

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