Antarctica - March 20, 2025 Credit: Nicole Hellessey Antarctica - Deep in the icy waters of the Southern Ocean, tiny krill are darting about in a frenzy at the mere whiff of penguin poo. Scientists have discovered that the smell of guano from these flightless birds sends Antarctic krill into a panic, swimming in fast zigzags to escape. Imagine the terror through the krill’s stalked compound eyes as a penguin, a streamlined predator, gobbles up thousands of them. Now, a new study reveals that even the water-borne stench of penguin droppings triggers dramatic escape behaviors. “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 Dr Nicole Hellessey, a researcher at Bigelow Laboratory for Ocean Sciences in Maine. Krill, a vital food source for many species and key carbon sequesterers, are crucial to the Antarctic ecosystem. With around 700 trillion adults in the Southern Ocean, their numbers are shifting south due to climate change and shrinking sea ice. Researchers aboard vessels in Antarctica’s Bransfield Strait collected krill in late 2022, keeping them alive in tanks. They also gathered 78g of smelly Adélie penguin guano from Torgersen Island, a revolting task according to Hellessey. In experiments at Palmer Station, krill were placed in a flume with dim light and flowing seawater mimicking their natural habitat. When exposed to water laced with penguin poo, the krill swam 1.5 times faster, made three times more turns, and slashed their algae intake by 64%. “Such behavior to escape from nearby penguins would greatly increase the krill’s odds of survival,” Hellessey explained. The frantic zigzagging, she believes, could spread through a swarm, amplifying their chances. What in the poo sparks this reaction remains a mystery, though Hellessey suspects it’s the scent of mashed-up krill and fish. She predicts similar responses near seals and whales. Worryingly, how warming oceans might dull this survival instinct is unknown, potentially shaking up the Southern Ocean’s delicate balance.