During the polar night, when the Sun does not rise for months, zooplankton across the Arctic stop following a 24-hour rhythm and switch to the Moon's 24.8-hour one instead.

They rise to feed in darkness and sink to hide from predators in light, and with no Sun the only light worth hiding from is the Moon's. Moorings across the whole Arctic basin recorded the entire community migrating on the lunar day, and diving deeper at full moon. It is the largest biological rhythm on the planet, and for part of the year the Moon is what sets it.