“Werewolf” Zooplankton Synchronise with the Light of the Full Moon

Research carried out in the Svalbard archipelago has shown that ecosystems previously thought to lie dormant during the long polar night are actually still active during this period, with entire communities synchronising their daily migration to the light of the full moon. Investigations are now taking place in order to find out what the implications of this previously undiscovered activity might be for the Artic ecosystem and environmental management of the area.

Diel vertical migration (DVM) has been said to be the largest synchronised movement of biomass on the planet. It is a common feature of all the world’s oceans (and most of the lakes) in which zooplankton migrate up to the surface layers of the water to feed under cover of darkness at night, and then return down into the deep to avoid being eaten during the day.

This process is, unsurprisingly, regulated by light. In most parts of the world, the rise and fall of the sun each day mediates DVM. However, a 2009 paper demonstrated that synchronised DVM was occurring in two fjords within the Arctic Circle during the polar night, a time when there is no direct light to control the behaviour. This discovery challenged the long-lasting paradigm of ecosystems at high altitudes becoming dormant during the polar night due to low food availability and lack of light, and prompted the creation of the CircA project by the paper’s authors.

Professor Jørgen Berge of the University of Tromsø and leader of CircA explains: “Although solar illumination is undetectable to the human eye during the polar night, our data indicates that Arctic zooplankton are still responding to the variations in low light levels. This means that there exists a whole suite of food-web interactions and ecosystem structural features that have simply been overlooked. We have now been working to establish the basic biological foundation behind the behaviours and their wider ecological impacts.”

One of the most fascinating findings from the project has been the importance of the moon. During the polar night, the zooplankton are no longer so strongly influenced by solar rhythm, and so during full moon – when the moon is at its brightest – they start to synchronise with the lunar rhythm instead. “What we see happen is that the zooplankton switch from a 24 hour cycle to a 24.8 hour cycle,” says Berge. “During full moon and on a clear night, the entire community will migrate deeper. It shatters the idea that the polar night is an environment entirely bereft of light and activity. The organisms in the water aren’t going into some kind of hibernation as was imagined – they are actively responding to the prevailing light climate.”

The team’s findings have sparked interest in the field and more research is now being done. Berge believes that one of the most important outcomes of his findings could be the implications that they have in the field of environmental management. Increased levels of shipping as well as oil and gas prospecting pose a threat to all Arctic wildlife, but having solid evidence that organisms are actively migrating during the polar night and are present at the surface rather than hibernating in deeper waters shows that any potential oil spill or similar accident could be highly damaging to the local ecosystem.