Nov 13

What if… Krill suddenly disappeared?

There can be few animals whose importance to the Earth’s ecosystem is as great as the Antarctic krill. The animal itself doesn’t look that impressive – it’s a small crustacean that looks rather like a shrimp – but what it lacks in its unassuming appearance, it more than makes up for in sheer abundance. In fact, the Antarctic krill makes up an estimated biomass of over 500 million tonnes, roughly twice that of all the humans in the world, which makes it, in this sense at least, the most successful animal on the planet.


Photo: Øystein Paulsen

Young krill make their way to the surface of the ocean soon after hatching and quickly form vast swarms. These swarms can stretch over an area of ocean equivalent to the size of several city blocks, up to 5 metres thick, and with as many as 60,000 krill per square metre. They accumulate not only for safety (they are eaten by a wide variety of animals, including the world’s largest, the blue whale) but also because their own food dwells in huge numbers by the surface: diatoms.

Diatoms are single-celled algae and they make up a large portion of the phytoplankton (‘plant drifters’). Since they photosynthesise to convert carbon dioxide and water into sugars, they need to float on the surface of the ocean to utilise the sun’s energy. They also coat the underside of the pack ice in the cold southern seas, forming upside-down lawns. The krill graze these pastures like tiny, multi-limbed cows, hiding away in the nooks and crannies of the pack ice to avoid large predators.


Composite image: Damián H. Zanette
Different species of diatoms

Crucial Krill

So now let’s assume that all of the krill in the world suddenly and mysteriously vanished from our oceans. What would happen? For a start, a large proportion of the marine ecosystem would collapse. Vast numbers of animals would find themselves with little to eat – not only the great filter-feeding whales, but also seals, penguins, squid and fish, which in turn would have a great impact on their own predators, such as orcas.

But the disappearance of the krill would also have more far-reaching consequences. You see, the digestive system of a krill is not particularly efficient. A large portion of the diatoms that the krill eat are egested without being properly broken down, and this waste drifts down to the bottom of the ocean. An unimaginably large amount of atmospheric carbon dioxide, utilised by the diatoms and then passed through the krill, is stored in this waste and therefore locked away in the sea floor for thousands of years. This process is massively important for the Earth’s climate.


Photo: Øystein Paulsen

Today we are seeing the consequences of a relatively small rise of carbon dioxide in the atmosphere, whether that be part of the planet’s natural cycle, our own doing, or a combination of the two. If these small yet incredibly important crustaceans vanished, not only would the ecosystems of the oceans crash, but more and more carbon dioxide would enter our atmosphere. This would cause runaway global warming, which would have a catastrophic effect on our poor planet. The oceans would become more acidic and much poorer in oxygen. The sea levels would rise and extreme weather, ranging from sudden cyclones and intense droughts, would become more and more commonplace.

So even if we weren’t bothered about the disappearance of the whales or the fish or the penguins, let us hope, for our sake if nothing else, that the lowly little krill aren’t suddenly whisked away. It wouldn’t end very well.


    • Luke on November 13, 2014 at 10:25 am
    • Reply

    Is there any known danger of krill disappearing? What would cause something like that?

    1. Krill aren’t currently endangered but their numbers have still fallen by as much as 80% in the past 40 years or so. The main cause is climate change. The Antarctic krill in particular feeds upside down on algae and diatoms on the underside of pack ice, but due to rising temperatures some of that ice has melted, so there are fewer places to feed from.

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