License to Krill: A shrinking resource

Antarctica is the coldest, driest, windiest, and highest continent, so it takes an impressive animals to call it home. What’s your favorite Antarctic species? Is it the majestic blue whale? The goofy emperor penguin? Perhaps the fierce leopard seal or killer whale?

Image credit: Pew Charitable Trusts

Now let me ask you this – what is the most important species in Antarctic waters?

If you guessed Antarctic krill, you’d be right.

Krill form the foundation of the Antarctic food web – nearly all of the animals we associate with the Southern Ocean feed either directly on krill or on a predator of krill. And even humans are getting in on the game. Last year, the Antarctic krill fishery produced nearly 250 thousand tons of krill (over 225,000 metric tons), primarily for krill oil supplements and fish feed.

But what exactly are krill?

Krill are small crustaceans (like shrimp or lobsters), generally the size of your thumb that feed on the phytoplankton associated with the underside of sea ice. In the Antarctic, they form dense swarms. So dense, in fact, that some scientists estimate that the combined mass of all the krill on the planet is more than that of any other species.

One of the most amazing things about krill is that these incredible animals can live up to seven years! Studies in the lab have shown that krill are actually able to reduce their metabolism in times of limited food availability by shrinking. Think about that for a minute. That would be like a lobster shedding its shell to become smaller when it didn’t have enough to eat. Talk about impressive!

Our understanding about this process, however, is quite limited. We know it can happen, based on studies in the lab, but it’s pretty difficult to study the animals living under the sea ice in an Antarctic winter.

Last month a study was published which used an ingenious method to overcome the difficulties of winter research. They recorded length measurements of krill captured on commercial fishing vessels across the region.

The study found that changes in adult krill lengths were only observed in females and shrinkage was observed even in areas not experiencing food deprivation. This means that poor feeding conditions may not be the only reason krill shrink in size. Instead, the authors propose that this could be a natural result of female sexual development.

Why is this important?

The case of the shrinking crustacean isn’t only an interesting example of weird biology – it’s also extremely important to our understanding of the Southern Ocean ecosystem.

In the Antarctic, the krill fishery is carefully managed by the Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR). While CCAMLR has been effective in managing the fishing pressure on Antarctic krill, there is still very little known about how much krill can be taken without affecting other species in the food web. Substantial work has begun on developing models addressing these concerns, but it seems that our understanding of krill biology is incomplete. Our lack of understanding their basic biology means that the population models we use to manage the fishery may be flawed.

To learn more about how world leaders are attempting to conserve Antarctic krill, check out this video from the Pew Charitable Trusts.

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