And, says National Geographic, it makes them take evasive maneuvers, ready to dodge their Antarctic predators:
In Antarctica’s Palmer Station lab, scientists put wild-caught krill through a series of tests to see if they could identify the presence of a predator—in this case, Adélie penguins—by squirting a slurry of penguin poop into the crustaceans’ tanks. Because there were just six to eight individuals in each test, the scientists were then able to measure the krill’s reactions.
“You could see straight away that they were having these avoidance behaviors,” says Nicole Hellessey, an Antarctic marine scientist at the University of Tasmania in Hobart, Australia and lead author of the new study published in Frontiers in Marine Science. “They’d start to zigzag all over the place.”
More specifically, the krill swam faster, with three times as many turns—and turns at sharper angles—than usual.
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But the discovery that krill can detect penguin guano, or excrement, in the water gives some potential answers to a big mystery. It may be the reason why the crustaceans give large, land-based penguin colonies a wide berth, despite the fact that when penguin poop washes into the sea, it triggers algal blooms, which krill love to eat.
It seems the buffer zone that krill avoid crossing is more evidence that the beady-eyed crustaceans know the predators are close, leading them to stay away.
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Climate change is also driving penguins to colonize new areas, or to stay in regions longer than they normally would, Hellessey notes. And that could lead to negative consequences for krill, given that the new study shows a dip in their feeding ability in the presence of penguins.