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.

 

HERE ARE THE FACTS:

Our fall fundraising drive is off to a rough start, and we very much need to raise $250,000 in the next couple of weeks. If you value the journalism you get from Mother Jones, please help us do it with a donation today.

As we wrote over the summer, traffic has been down at Mother Jones and a lot of sites with many people thinking news is less important now that Donald Trump is no longer president. But if you're reading this, you're not one of those people, and we're hoping we can rally support from folks like you who really get why our reporting matters right now. And that's how it's always worked: For 45 years now, a relatively small group of readers (compared to everyone we reach) who pitch in from time to time has allowed Mother Jones to do the type of journalism the moment demands and keep it free for everyone else.

Please pitch in with a donation during our fall fundraising drive if you can. We can't afford to come up short, and there's still a long way to go by November 5.

payment methods

ONE MORE QUICK THING:

Our fall fundraising drive is off to a rough start, and we very much need to raise $250,000 in the next couple of weeks. If you value the journalism you get from Mother Jones, please help us do it with a donation today.

As we wrote over the summer, traffic has been down at Mother Jones and a lot of sites with many people thinking news is less important now that Donald Trump is no longer president. But if you're reading this, you're not one of those people, and we're hoping we can rally support from folks like you who really get why our reporting matters right now. And that's how it's always worked: For 45 years now, a relatively small group of readers (compared to everyone we reach) who pitch in from time to time has allowed Mother Jones to do the type of journalism the moment demands and keep it free for everyone else.

Please pitch in with a donation during our fall fundraising drive if you can. We can't afford to come up short, and there's still a long way to go by November 5.

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