Baby krill living around Antarctica are struggling to cope with rising sea temperatures, new research suggests.
The study, published online Jan. 21 in the journal Nature Climate Change, shows that fewer of the tiny, shrimp-like Antarctic krill (Euphausia superba) are surviving to adulthood in the northern reaches of the Scotia Sea, home to the largest concentrations of the animal.
“These northern waters have warmed and conditions throughout the Scotia Sea have become more hostile, with stronger winds, warmer weather and less ice,” Simeon Hill, an ecologist at the British Antarctic Survey and one of the paper’s lead authors, said in a statement. “This is bad news for young krill.”
Hill and his colleagues pulled together data on the body lengths and counts of individual krill in the Southern Ocean going back more than 90 years. They zeroed in on the Scotia Sea where the Atlantic and Southern Oceans meet. Historically, that’s been the best spot to find dense clouds of krill, which are a critical food source for fish, penguins and whales.
Scientists have tracked the shift of zooplankton like krill toward cooler waters around both poles as a result of climate change. But without the type of comprehensive data sets used in this study, it’s been difficult to determine how large an effect warmer temperatures are having now or will have in the future, the authors write.
“It is only when we put all our data together that we can look at the large scales of space and time to learn how populations of key polar species are responding to rapid climate change,” Angus Atkinson, a marine ecologist at Plymouth Marine Laboratory in the U.K. and a lead author of the study, said in the statement.
In the Scotia Sea, they found that the highest densities of krill had shifted southward by some 440 kilometers (273 miles) since the 1920s.
“Most of this contraction seems to have occurred since the 1970s,” the authors write.
Over that same time period, however, the average size of adult krill grew by 6 millimeters (0.24 inches), translating to 75 percent heavier animals. The authors say this size increase is likely a result of having fewer young krill around rather than a direct effect of warmer waters. It’s also an indication that krill face “increasing difficulty in replenishing itself and maintaining high numbers at the northern edge of the Southern Ocean,” Hill said.
Those changes to the demographic makeup of the krill population have the potential to shake up the region’s food web, if, for example, these larger krill can swim faster or they start hanging out in deeper, colder waters, the researchers write.
The drop in northerly krill densities mirrors trends in other parts of the food web: A 2014 study linked climate change to lower birth weights in fur seals living around South Georgia Island, which sits in the northern part of the Scotia Sea.
The authors also point out that the internationally managed krill fishery, which supplies food for aquarium fish as well as people, has “conservative catch limits,” but that they don’t reflect the location and size of the krill population yet. In March 2018, the environmental organization Greenpeace said fishing vessels were competing with wildlife for krill around the Antarctic Peninsula. Then, in July, most companies said they would stop krill fishing in that part of the Southern Ocean.
Atkinson, A., Hill, S. L., Pakhomov, E. A., Siegel, V., Reiss, C. S., Loeb, V. J., … & Sailley, S. F. (2019). Krill (Euphausia superba) distribution contracts southward during rapid regional warming. Nature Climate Change, 9(2), 142–147.
Forcada, J., & Hoffman, J. I. (2014). Climate change selects for heterozygosity in a declining fur seal population. Nature, 511(7510), 462.