It is cold out! However, while it is cold the days are also clear and sunny and the night sky is full of stars. I have taken many a beautiful walk in winter wonderland enjoying the sparkle of light on the snow and ice crystals or marveling at formations of ice sculpted by the trickle of what once were flowing creeks and streams and waterfalls. While it has become cumbersome to walk on any sidewalk, I discovered that the frozen surfaces of lakes have become a new alternative place to take my dog for her daily outings.
The very places where I stood last summer and watched sticklebacks and young salmon dart around to hide among green and brown water plants or catch a little bug with tiny wings stuck to the water surface have now turned to solid ice. What has happened to the abundant life? Where did the fish go? Where are the tiny bugs? How do they make it through these frozen times?
Consider studying the question of where the fish are and how they survive through a cold winter in a frozen lake. How would you get your samples? If you had questions that required observing live animals, how would you mimic the winter conditions in an experiment? Studying a winter lake is much much more complicated and even dangerous than studying a lake in summer. Thus, it is no great surprise that we know much less about what happens in winter than we do about spring, summer and fall.
In the absence of samples and good data, scientists do what all of us do on a daily basis in similar situations: They make their best educated guess. History is full of great educated guesses, some of them held up better in the evolution of knowledge than others. The Earth is flat and when you get to the edge you fall off. Lightning is caused by a divine being getting angry. Geese dive to the bottom of lakes to overwinter. The emission of carbon dioxide gas into the atmosphere changes the climate on earth (this was first observed in experiments by John Tyndall in 1859).
For the longest time has winter been the off season for researchers studying lake ecosystems. Recently, an international team of researchers has tackled the difficulties of studying what happens in lake ecosystems under the winter ice. They were trying to test how well the educated guess that all life enters a state of deep snow-white sleep would hold up against real life testing.
Surprisingly, it didn’t. The researchers quickly discovered that life is much more active under the ice than previously thought. Still, the energy for life comes from the sun and in places where the ice is clear and more sunlight penetrates, more production happens in winter by so-called ice algae. These are photosynthetic algae that use the underside of the ice to attach to or float nearby. A clear ice sheet may act like a window shielding these algae from the disturbances of waves and turbulences. The research team describes a layer of filamentous algae under the ice and a community of small plankton feeding on those algae.
If you have ever gazed out of the window of a plane while it was sailing along just over a cloudy sky, you can picture the cotton-like appearance of those clouds like something you would love to let yourself fall into. Imagine those clouds hanging above you under a ceiling of glass and now imagine them glowing bright green. The picture that presented itself to the under-ice divers who studied winter Lake Baikal appears almost psychadillic.
What the researchers found was surprising and means that wintertime is not necessarily an off time for the production and life cycles in lakes. However, the rules of energy transfer still apply and if there is no light that penetrates the ice then algae can not thrive.
Until I find out otherwise I am going to assume that the sticklebacks have moved to deeper areas of the lake where the water remains unfrozen, the tiny salmon have grown up a little and are likewise hiding in debris around the shorelines of the lake under the ice. Their metabolism has probably slowed down and they eat very little, mostly the remaining plankton from last summer’s crop. Those plankton organisms have deposited their eggs in the bottom mud, where they are safe and snug ready to hatch when the ice releases the lake and more and more sunlight gets through.
Just like I have found my ways to survive my winter explorations huddled up in a warm coat, gloves and hat, so these animals have all found their own amazing methods to live in their environment which is covered in ice in the winter.