'Werewolf' creatures in the Arctic navigate by the cycle of the MOON: During dark winter months plankton migrate in lunar cycles
- Absence of sunlight in the Arctic during the winter months leads to zooplankton adopting a 'lunar day' of 24.8 hours
- Further monthly cycle of 29.5 days coincides with full moon and high tides
- Findings are the same throughout the Arctic, even under pack ice
- Researchers likened the mass migrations to 'behaviour of werewolves'
It is one of the greatest migrations on the planet, but one that has, until now, remained somewhat mysterious.
Countless millions of zooplankton feed each night near the surface of the ocean but, to escape being eaten themselves, make a daily commute to the dark depths when the sun comes out.
Now scientists have discovered that, in the icy waters of the far north where they can't rely on the rising of the sun, this daily cycle follows a different rhythm, driven by the moon.
Zooplankton feed each night near the surface of the ocean but, to escape being eaten, make a daily commute to the dark depths when the sun rises. Now scientists have discovered that, in the icy waters of the Arctic where they can't rely on the rising of the sun, this daily cycle follows a different rhythm, driven by the moon
In the Arctic during the winter, the region is without sunlight for months at a time.
Plankton in the Arctic still make their regular migrations to and from the safety of the deep, but rather than doing it as the sun rises, they adopt a 'lunar' 24.8-hour schedule.
Instead of waiting for the sun to rise, during these dark months the zooplankton's vertical migrations take place when the moon rises above the horizon.
This is because the predatory creatures that hunt them see by moonlight rather than sunlight.
'The most surprising finding is that these migrations are not rare or isolated to just a few places,' says Dr Kim Last of the Scottish Association for Marine Science (Sams).
'During the permanently dark Artic winter, these tiny creatures, like mythical werewolves, respond to moonlight by undergoing mass migrations.'
No matter where the researchers looked during the Arctic winter – in fjord, shelf, slope, or open sea – they observed the same behaviour.
In the Arctic during the winter, the region is without sunlight for months at a time. Plankton in the Arctic still make their regular migrations to and from the safety of the deep, but rather than doing it as the sun rises, they adopt a 'lunar' 24.8-hour schedule
These lunar migrations happen every winter at all sites, even under sea ice with snow cover on top. In addition to this daily cycle, they also discovered a mass sinking of zooplankton (picutred) from the surface waters to a depth of about 164ft (50 metres) every 29.5 days in the winter
These lunar migrations happen every winter at all sites, even under sea ice with snow cover on top.
In addition to this daily cycle, they also discovered a mass sinking of zooplankton from the surface waters to a depth of about 164ft (50 metres) every 29.5 days in the winter.
This coincided with the full moon.
Rather than returning after dark, at this time of the month the plankton remained in the depths for five or six days.
Among the predators they seek to escape are hunter-killer plankton such as Themisto libellula.
Dr Last and his team think their findings may have important implications for the carbon cycle, particularly in light of climate change.
'The daily vertical migration of zooplankton contributes significantly to the carbon pump by moving fixed carbon from the surface into the deep ocean,' Dr Last explained.
'Since there is no photosynthesis during the polar night, carbon is only moved into the deep by predators feeding on prey.'
As the climate changes and the ice melts, Dr Last said, lunar-driven zooplankton migrations might 'become more prevalent, though as yet, we do not know the consequences of this.'
Among the predators they seek to escape are hunter-killer plankton such as Themisto libellula (pictured). Dr Last and his team think their findings may have important implications for the carbon cycle, particularly in light of climate change
Zooplankton are not the only animals to navigate using the moon.
Scientists recently found a nocturnal species of beetle uses moonlight as a form of compass to roll balls of excrement in a straight line.
By looking at the beetle’s brain cells, they found that ‘compass neurons’ respond to the position of the sun during the day, but switched to respond to polarised light during the night.
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