In lab experiments, the mere scent of penguin droppings — or guano — sent krill scrambling for escape, researchers report March 20 in Frontiers in Marine Science. The stink also seemed to suppress krill’s appetites.

Antarctic krill (Euphausia superba) form a cornerstone of the Southern Ocean ecosystem. “They’re the main food source for all of the big, charismatic fauna,” says Nicole Hellessey, an Antarctic marine scientist at the University of Tasmania in Hobart. Whales, penguins and seals all eat — or eat things that eat — krill. Understanding the critters’ movements could help identify key areas for marine conservation.

Krill use their antennae to sniff out food, mates and even pollution. But scientists weren’t sure if they could detect predators by scent. To find out, Hellessey and her colleagues netted krill off the Antarctic Peninsula and transported them to nearby Palmer Station.

In the lab, the team let krill loose in a flume filled with flowing seawater, adding either algae for the krill to eat, a bit of Adélie penguin poop or both. Cameras tracked the krill’s 3-D movement.

Working with the krill was fun, says oceanographer David Fields of the Bigelow Laboratory for Ocean Sciences in East Boothbay, Maine. “They truly are these cute, charismatic animals.”

Working with penguin poop was another story. “Penguin crap is the most vile thing you can imagine,” Fields says. Just opening guano storage bags “would clear the entire lab space.” 

Krill showed a similar reaction to the smell. In algae-only water, they quickly swam toward the food then lingered near the buffet. But in water with algae and guano, the krill zigzagged, Hellessey says. “They’d sort of dart in, eat and dart out.” Krill swam in frantic zigzags in water containing only penguin poop, too.

A second set of experiments placed krill in seawater buckets with either algae or algae plus guano. Over 22 hours, krill in the algae-only buckets ate about 67 percent of the food. Krill in buckets with penguin poop ate only about 25 percent.

The scientists aren’t sure what aromas in penguin feces the krill are reacting to. But since Adélie penguins’ diets are over 99 percent krill, “a lot of that guano would have crushed-up krill sort of scents,” Hellessey suspects. Some chemical cue might make the krill go, “‘Oh my god, my buddy’s hurt, I shouldn’t go over there.’”