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Although a single penguin is capable of devouring thousands of krill in a single sitting, swarms of the zooplankton may detect disturbances in the water ahead of mealtime. The telltale sign? Bird poop.
That’s what researchers at the Bigelow Laboratory for Ocean Sciences theorize after studying the movements of krill trawled from Antarctica’s Bransfield Strait. According to their results, published March 20 in Frontiers in Marine Science, it only takes a small amount of penguin guano (poop) to influence the tiny sea creatures’ behavior.
“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,” Nicole Hellessey, a corresponding author and postdoctoral researcher, explained in an accompanying statement.
To test how krill respond to chemical evidence of nearby penguins, Hellessey and colleagues placed krill into an aquarium at Palmer Station on Antarctica’s Anvers Island. They then separated out six-eight individuals and transferred them into a flume of seawater measuring 34.7 degrees Fahrenheit. To better replicate their usual environment, the team even dimmed the ambient lighting to mimic a depth of around 131 feet. Over multiple trials, researchers funnelled in seawater mixed with either algae, penguin poop, or a mixture of both while recording the results using a pair of automated cameras. Scientists then analyzed the footage based on selected krills’ 3D positionality as well as the direction and speed of their swimming.
The findings were clear. While krill generally swim straight upstream in what’s known as rheotaxis, the presence of penguin guano appeared to immediately influence their behavior. More specifically, the krill sped up their swimming as much as 1.5 times faster than average while also making three times more turns at larger angles.
The penguin poop didn’t only influence krill movements. In another phase of the experiment, researchers noticed the zooplankton consumed 64 percent less algae after sensing what they thought may be nearby birds. This implies that krill engage in evasive maneuvers so much that they subsequently eat less when guano is in the water around them.
“Such behavior to escape from nearby penguins would greatly increase the krill’s odds of survival,” said Hellessey. “And these odds would increase exponentially in a swarm, if their neighbors could detect the same cues and communicate the danger to each other.”
The defensive response is likely not only limited to penguins. Given the range of predators that regularly feed on krill, the team theorizes they likely exhibit similar behavior in the presence of seals, whales, and other Antarctic predators.
As climate change continues to shift global ocean ecosystems, however, this detection ability may reduce a krill’s chances for survival. Although the team hasn’t identified the specific chemicals present in penguin poop that sends krill into a panic mode, they do know that rising acidification levels and warming temperatures could affect how the zooplankton sense danger.
“Any changes to krill’s behavior could have major impacts on the future Southern Ocean, as Antarctic krill are a keystone species in this ecosystem,” Hellessey said.
Regardless of further research results, one thing is apparently certain: Dealing with penguin poop is not an enjoyable experience.
“Smells like rotten shellfish. Not pleasant to handle,” warned Hellessey.
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