Scientists have found that just like humans, krill respond to changes in light levels.
Researchers studying the visual sensitivity of the animals in the waters off Svalbard have found that when light levels are up, the krill swim to darker depths to shelter from predators. When light levels are low, they come up to find their food sources which are often bioluminescent.
The researchers looked at light sensitivity in krill during the Arctic polar night. According to Jonathan Cohen, lead author of the research and associate professor at the University of Delaware’s School of Marine Science and Policy:
“The dogma for a long time was that when the sun stays below the horizon, biology just goes into suspended animation, and then everything kicks back up again when the sun comes back above the horizon in the spring. Our work has found that is not the case. Instead, you’ve got organisms that are active throughout that polar night period when the sun is below the horizon. There is also more light than you would think, even when the sun is below the horizon, and it has biological impacts.”
Researchers found that the krill used these as visual keys in multiple ways. Also, the krill use the light level to control their own bioluminescence to avoid being eaten by predators.
You can check out their research here.