In the absence of sunlight, the Moon drives the vertical migrations of tiny marine animals through the permanently dark and frigid Arctic winter, a new study has found.
Researchers said that the behaviour is most likely an attempt by zooplankton to avoid predators hunting by moonlight.
“During the permanently dark and extremely cold Artic winter, these tiny marine creatures, like mythical werewolves, respond to moonlight by undergoing mass migrations,” said Kim Last from the Scottish Association for Marine Science in Scotland.
No matter where the researchers looked during the Arctic winter - in fjord, shelf, slope, or open sea - they observed the same behaviour.
Further investigation showed that the marine creatures had shifted their activities from following the 24-hour solar day to following the 24.8-hour lunar day.
In winter, zooplankton’s vertical migrations take place when the Moon rises above the horizon, researchers said.
In addition to this daily cycle, they also discovered a mass sinking of zooplankton from the surface waters to a depth of about 50 meters every 29.5 days in the winter, coinciding with the full Moon.
“The most surprising finding is that these migrations are not rare or isolated to just a few places,” said Last.
“The acoustic database used for our analysis cumulatively spans 50 years of data from moorings that cover much of the Arctic Ocean. The occurrences of lunar migrations happen every winter at all sites, even under sea ice with snow cover on top,” he added.
The daily vertical migration of zooplankton contributes significantly to the carbon pump by moving fixed carbon from the surface into the deep ocean, researchers said.
“Since there is no photosynthesis during the polar night, carbon is only moved into the deep by predators feeding on prey,” said Last.
According to researchers, this influence of zooplanktons’ winter movements will need to be quantified and incorporated into biogeochemical models. The findings were published in the journal Cell Press.