Seal Fur Sheds Light on Antarctic Krill

Antarctic fur seal (right), Weddell seal (left), Penguin Island, South Shetland Islands, Antarctica.: Credit: © Julia Whitty.Antarctic fur seal (right), Weddell seal (left), Penguin Island, South Shetland Islands, Antarctica.: Credit: © Julia Whitty.How do you assess the health of a marine invertebrate—namely Antarctic krill—when there’s no historical baseline to measure it against?

In an intriguing piece of detective work reported in PLoS ONE a team of researchers from China and the US turned to analyzing old seal hairs to determine changes in abundance of krill in the past century.

Antarctic krill.: Credit: Uwe Kils via Wikimedia Commons.Antarctic krill.: Credit: Uwe Kils via Wikimedia Commons.

Antarctic krill, Euphausia superba, is a keystone species in the Southern Ocean and the primary consumer in a foodweb supporting fish, penguins, seabirds, seals, and whales. They school in swarms of up to of 30,000 individuals per cubic meter and are perhaps the most abundant animal on Earth, with a total biomass estimated at ~379 million metric tons.

In the video below (starting at 00:01), you can see humpback whales bubble feeding on krill in Antarctic waters. 

 

There’s evidence of a decline in krill biomass in parts of Antarctica in the past 30 years—but when did it begin?

To look deeper into history, the authors analyzed core samples from lake sediments near an Antarctic fur seal colony on King George Island in the South Shetland Islands off the Antarctic Peninsula. They dated the fur in the cores via stable carbon (δ13C) in the samples. They inferred the abundance of krill in the seals’ diet via the nitrogen (δ15N) isotopes in the fur. From the paper:

Since Antarctic fur seals feed preferentially on krill, the variation of [nitrogen] in seal hair indicates a change in the proportion of krill in the seal’s diets and thus the krill availability in local seawater.

 

Antarctic krill grazing on algae living on the underside of sea ice.: Credit: Uwe Kils via Wikimedia Commons.Antarctic krill grazing on algae living on the underside of sea ice.: Credit: Uwe Kils via Wikimedia Commons.Their results indicate that krill began to decline in the diet of fur seals in this part of Antarctica nearly a century ago. That time frame correlates with increasing sea surface temperatures and dwindling sea ice. (See my post Life Inside the Sea Ice for more about the relationship between krill and sea ice.) From the PLoS ONE paper:

In this region for the past decades, the sea ice shows a decline trend, and this is in coincidence with the decline trend in krill populations. Like the seal [nitrogen] values, the sea surface temperature (SST) anomaly in Southern Ocean (50°S) also shows an obvious increasing trend for the 20th century, and the significant correlation between them… suggests that the inferred decreasing krill population is linked with warming ocean and declining sea ice extent.

 

 

 The paper: 

  • Huang T, Sun L, Stark J, Wang Y, Cheng Z, et al. Relative Changes in Krill Abundance Inferred from Antarctic Fur Seal. PLoS ONE. 2011. DOI:10.1371/journal.pone.0027331.

 

AN IMPORTANT UPDATE

We’re falling behind our online fundraising goals and we can’t sustain coming up short on donations month after month. Perhaps you’ve heard? It is impossibly hard in the news business right now, with layoffs intensifying and fancy new startups and funding going kaput.

The crisis facing journalism and democracy isn’t going away anytime soon. And neither is Mother Jones, our readers, or our unique way of doing in-depth reporting that exists to bring about change.

Which is exactly why, despite the challenges we face, we just took a big gulp and joined forces with the Center for Investigative Reporting, a team of ace journalists who create the amazing podcast and public radio show Reveal.

If you can part with even just a few bucks, please help us pick up the pace of donations. We simply can’t afford to keep falling behind on our fundraising targets month after month.

Editor-in-Chief Clara Jeffery said it well to our team recently, and that team 100 percent includes readers like you who make it all possible: “This is a year to prove that we can pull off this merger, grow our audiences and impact, attract more funding and keep growing. More broadly, it’s a year when the very future of both journalism and democracy is on the line. We have to go for every important story, every reader/listener/viewer, and leave it all on the field. I’m very proud of all the hard work that’s gotten us to this moment, and confident that we can meet it.”

Let’s do this. If you can right now, please support Mother Jones and investigative journalism with an urgently needed donation today.

payment methods

AN IMPORTANT UPDATE

We’re falling behind our online fundraising goals and we can’t sustain coming up short on donations month after month. Perhaps you’ve heard? It is impossibly hard in the news business right now, with layoffs intensifying and fancy new startups and funding going kaput.

The crisis facing journalism and democracy isn’t going away anytime soon. And neither is Mother Jones, our readers, or our unique way of doing in-depth reporting that exists to bring about change.

Which is exactly why, despite the challenges we face, we just took a big gulp and joined forces with the Center for Investigative Reporting, a team of ace journalists who create the amazing podcast and public radio show Reveal.

If you can part with even just a few bucks, please help us pick up the pace of donations. We simply can’t afford to keep falling behind on our fundraising targets month after month.

Editor-in-Chief Clara Jeffery said it well to our team recently, and that team 100 percent includes readers like you who make it all possible: “This is a year to prove that we can pull off this merger, grow our audiences and impact, attract more funding and keep growing. More broadly, it’s a year when the very future of both journalism and democracy is on the line. We have to go for every important story, every reader/listener/viewer, and leave it all on the field. I’m very proud of all the hard work that’s gotten us to this moment, and confident that we can meet it.”

Let’s do this. If you can right now, please support Mother Jones and investigative journalism with an urgently needed donation today.

payment methods

We Recommend

Latest

Sign up for our free newsletter

Subscribe to the Mother Jones Daily to have our top stories delivered directly to your inbox.

Get our award-winning magazine

Save big on a full year of investigations, ideas, and insights.

Subscribe

Support our journalism

Help Mother Jones' reporters dig deep with a tax-deductible donation.

Donate