If youve walked past the penguin exhibit at the zoo, then youve likely caught a whiff of their unpleasant-smelling poo. The smell has perhaps made you want to cover your nose and, despite a penguins cuteness, want to walk away.Humans arent the only ones repelled by penguin poo, however. To krill, tiny shrimp-like creatures, the smell of penguin poo triggers evasive maneuvers, probably because they know that penguins are on their way to eat them. After putting it to the test, a research team has determined that a chemical within the poo causes krill to act erratically, according to a recent study published in Frontiers in Marine Science.Krill and their Scent TriggersAdlie penguins (Pygoscelis adeliae)(Image Credit: Nicole Hellessey)Krill are a keystone species in Antarctica and, unfortunately for them, they reside near the bottom of the food chain. They provide food for some marine species and one of those species is the Adlie penguin. According to the study, these penguins consume 1.6 kg (about 3.5 pounds) of krill per day, and theAdlie penguin population as a whole consumes about 1.5 trillion tons of krill annually.Krill are sensitive to chemicals in their environment. They rely on these triggers to find food and mates but also to adapt to environmental stressors like pollution and now, according to the new study, predators. According to the research team, a chemical in the Adlie penguins poo can trigger krill into evasive maneuvers.A Krill ExperimentFor the study, the research team collected krill from the Southern Ocean and brought them to a lab. There, the krill were kept in tanks and fed an algal slurry. During the experiment, the team placed six to eight krill together in a flume of seawater and manipulated the light and temperature so that it was the same as in the wild.From there, researchers then fed three types of water through the flume to mimic the oceans constant movement. Each of the three types of water contained either algae, penguin poo, or a mixture of both. After testing each group four times, the team found that krill reacted strongly to the scent of the penguin poo.Here we show for the first time that a small amount of penguin guano causes a sudden change in the feeding and swimming behaviors of Antarctic krill, said Nicole Hellessey, a postdoctoral researcher at the Bigelow Laboratory for Ocean Sciences in Maine, and the corresponding author of the study, in a press release.While krill typically swim in a head-on, straight line, after scenting the poo, they began to swim faster and made more frequent turns.Read More: How Do Penguin Wings Reach High Speeds Underwater?A Chemical ReactionBesides their change of speed and direction, the team also noticed that the krill displayed different feeding patterns after being exposed to the poo. According to the study, the krill reduced their consumption of algae by 64 percent when the poo was in the water, probably due to their frequent irregular, zig-zag movements.Such behavior to escape from nearby penguins would greatly increase the krills odds of survival. And these odds would increase exponentially in a swarm if their neighbors could detect the same cues and communicate the danger to each other, said Hellessey in a press release.However, what remains a mystery is which specific chemical in the poo causes this reaction? The research team has yet to determine it.We don't yet know how the ability of krill to sense these chemical cues and their escape behavior towards them might vary when diluted in open waters, or under global warming or ocean acidification conditions, Hellessey said in a press release. Any changes to krills behavior could have major impacts on the future Southern Ocean, as Antarctic krill are a keystone species in this ecosystem.Article SourcesOur writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:A graduate of UW-Whitewater, Monica Cull wrote for several organizations, including one that focused on bees and the natural world, before coming to Discover Magazine. Her current work also appears on her travel blog and Common State Magazine. Her love of science came from watching PBS shows as a kid with her mom and spending too much time binging Doctor Who.