When Antarctic krill swarm, the semi-transparent shrimp-like crustaceans join together in the millions or trillions, forming dense coral-colored underwater clouds as they swim in sync with one another and traverse frigid ocean currents. Some of these swarms are so large they can be seen from space, extending for miles near the ocean’s surface and hundreds of feet below, attracting predators from land, sea and sky.
Individually, each of these animals is only about two inches long, but collectively they form one of the largest biomasses on the planet. They also fuel the entire food web in the Southern Ocean, which circles Earth’s southernmost continent. “Every single species in Antarctica feeds on krill, or something that feeds on krill,” said Rodolfo Werner, a marine biologist from Argentina who has been studying marine ecosystems in Antarctica for more than 20 years.
But the crustacean’s future, and that of its predators, by extension, are increasingly in jeopardy due to climate change and a growing commercial krill fishery. Rising air and sea temperatures are causing krill’s icy habitat that they rely on for food and shelter to melt, especially in their early life.
Krill larvae feed on algae that grows on the underside of frozen seawater floating near the ocean’s surface. “They graze on the sea ice like cows,” said Werner. But, in the last two years, sea ice coverage in Antarctica has shrunk to historic lows due to rising air and sea temperatures, according to the National Snow and Ice Data Center at the University of Colorado Boulder.
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