Planet Earth Online

Arctic plankton just keep on moving... even in the depths of winter

23 October 2008

Above 80 degrees north - well within the Arctic Circle - winters are unforgiving. So unforgiving that the sum of our knowledge of the biology of the millions of microscopic marine animals that call the Arctic Ocean home is practically zero. This is because it's not easy to work in such a dark, cold, inhospitable environment.

One of the aims of International Polar Year (IPY), which runs from 2007 to 2009, is to make some headway into filling the gap in our scientific knowledge of polar regions.

Now some of the first research on Arctic winter marine ecology to come out of IPY challenges the long-held idea that a major Arctic biological process to all intents and purposes shuts down.

Most predators use light to see their prey, so canny zooplankton - tiny animals near the bottom of the marine food chain - feed at the ocean surface during darkness and move to the safety of the depths of the ocean during daylight hours to avoid being eaten. It's the biggest synchronised shift of biomass on the planet.

Scientists assumed that because the sun either never rises or is extremely low in the sky during the polar winter, the lack of light meant that zooplankton wouldn't need to move up and down in the ocean, but instead would just hibernate in deep water.

Not least because during the winter, the phytoplankton that zooplankton feed on scarper when the sunlight they need to make their food using photosynthesis disappears.

New research published today in Biology Letters reveals that zooplankton continue their daily pattern moving up and down in the ocean, although to a slightly lesser extent, as if it's the middle of summer. Although, in ocean that's covered in ice, their movement through the depths is dampened down.

"We knew nothing about how zooplankton move around in the ocean during the Arctic winter before this, because there are hardly any studies on the subject," says the scientist who led the study, Jørgen Berge, from the Scottish Association for Marine Science.

The researchers say it's possible that zooplankton are much more sensitive to light than we are. Even in the darkness of winter, they may still be able to figure out when's day and when's night.

But with very little to feed on and hardly any light making their predators' jobs even harder, the researchers are now eagerly trying to figure out why zooplankton persist with their daily up-and-down rhythm.

Although the research throws up a lot of questions, finding out more about the biology of zooplankton is a step closer to understanding how carbon moves around the Arctic Ocean during the winter months.

Keywords: Arctic, Biodiversity, Environmental change, Oceans, Polar,

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