Krill loss could be ‘catastrophic’ for polar food chain

Phytoplankton are the main food for krill, the tiny crustaceans that sustain many species, including fish and whales. "There's a domino effect: changes in large-scale patterns, changes in wind and sea ice, and then changes in phytoplankton, at the bottom of the web," says Grace Saba. (Credit: The Sun and Doves/Flickr)

Changes in wind and sea ice cover in the rapidly warming Western Antarctic Peninsula have the potential to affect the food chain—from single-cell organisms to the humpback whale.

“The more we understand how the physical environment is tied to the food web, the better we will understand how long-term changes in climate will impact the ecosystem,” says Grace Saba, the study’s lead author.

krill swarm
(Credit: Rutgers)

Saba, an assistant research professor in the School of Environmental Science’s Institute of Marine and Coastal Sciences, examined the correlation between changes in climate and the abundance of marine life over a 21-year period. It’s one of the few instances where marine researchers have a dataset of sufficient length and detail to reveal how climate signals can affect a polar food web.

Domino effect

Rutgers scientists began studying the fast-changing region in 1991. Saba’s co-authors include Oscar Schofield, a professor of marine science. Saba and Schofield are members of the Palmer Long-Term Ecological Research program.

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The program conducts annual shipboard surveys along the western side of the Antarctic Peninsula, including the coastal ocean near Palmer Station, one of the three US research stations in Antarctica. The station was established more than two decades ago to study changes and processes that couldn’t be captured in a single expedition or research cruise.

At the center of the study published in Nature Communications is the belt of low pressure, experienced as westerly winds, that surrounds the Antarctic continent. The belt, called the Southern Annular Mode or Antarctic Oscillation, moves north and south on a four- to six-year cycle, which affects physical factors such as wind and sea ice cover.

“There’s a domino effect: changes in large-scale patterns, changes in wind and sea ice, and then changes in phytoplankton, at the bottom of the web,” says Saba.

Phytoplankton are the main food for krill, the tiny crustaceans that sustain many species, including fish and whales. When the Southern Annular Mode is negative (high pressure over the Antarctic, low pressure over mid-latitudes), cold southerly winds blow across the peninsula, sea ice cover increases and phytoplankton multiply, leading to higher krill recruitment—the addition of new, young individuals into the krill population—according to Saba’s research.

In contrast, during a positive phase of the Southern Annular Mode, there is less ice, less phytoplankton and lower krill recruitment, which means less food for all other animals up the food chain.

“Krill live five to seven years,” Saba says. “Their evolution could be tied to cycles in the Southern Annular Mode. If they have a good year, that’s great. But if they miss even one cycle, that could be catastrophic to their population.”

The National Science Foundation helps support Palmer Station research.

Source: Rutgers University