A key food source for Antarctic seals, whales and penguins has declined about 80 percent since the 1970s in ocean waters near the Antarctic Peninsula, researchers report.

The overall effect of the decline in stocks of krill, a shrimp-like crustacean, isn’t clear, but the finding suggests “we need to do some more work quite urgently to find out what’s going to happen,” said marine biologist Angus Atkinson.

Atkinson, of the British Antarctic Survey, is lead author of a report on krill abundance in Thursday’s issue of the journal Nature.

He and colleagues combined data from nearly 12,000 net hauls done from 1926-39 and 1976-2003. Results showed the Antarctic krill population to be concentrated largely northeast of the Antarctic Peninsula, which lies south of the tip of South America, but they also revealed the long-term declines in summer krill stocks in this area.

Statistical analysis suggested the most likely explanation is declines in the amount of winter sea ice in the area of the peninsula. Krill feed on algae found on sea ice.

The area around the peninsula has shown an unusually strong warming trend over the past 50 years, although Atkinson said it’s not clear how that is connected to the loss of sea ice. He also said the cause of the warming isn’t known.

Eileen Hofmann, professor of oceanography at Old Dominion University in Norfolk, Va., said if the study is born out by further work, it means climate change is affecting the marine food web in the Antarctic Peninsula region.

It will take more research to determine the impact on penguins, seals and whales, she said.

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