Seasonal magic under the water
Compared to the abundant wildlife we see during the warm summer months, it’s easy to assume that life becomes “frozen” once the temperature drops; however, lake ecosystems are very much still active during the winter.
The weird world of zooplankton
“But if, retaining sense and sight, we could shrink into living atoms and plunge under the water, of what a world of wonders should we then form part! We should find this fairy kingdom peopled with the strangest creatures – creatures that swim with their hair, that have red ruby eyes blazing deep in their necks, …and there are others flashing by in glass armour, bristling with sharp spikes or ornamented with bosses and flowing curves.”
This is a wonderfully poetic and accurate description of zooplankton by Charles Thomas Hudson in his 1889 book, “The Rotifera.” Zooplankton are a diverse group of tiny animals that live below the water’s surface. They range in size from a few microns up to a few millimeters and many of them are almost fully translucent to avoid being eaten. Zooplankton are an essential link between the bacteria and photosynthetic algae at the bottom of a lake’s food web and the upper parts of the food web occupied by fish.
It was once thought that almost all zooplankton entered resting stages and were uncommon in the water column once winter set in and ice formed. The idea was that the conditions were too unfavorable due to low light levels under ice and snow, low food supply, and low temperatures. However, recent research reveals that the ice itself can support overwintering plankton communities. Some algae grow on the underside of the lake ice where they find habitat and sufficient light for photosynthesis. This activity allows bacteria and zooplankton to thrive in icy conditions, albeit at lower abundances than during the summer. If food becomes scarce some zooplankton can also use fatty reserves to keep them going.
Sleepy turtles and frogs
Turtles have lungs and are cold-blooded, meaning their internal temperature adjusts to match the temperature of their environment. So, how can they possibly survive in freezing cold lakes covered in ice? As lakes begin to freeze, they burrow in the mud and slow their metabolism. Since they aren’t moving around frequently, they don’t use as much energy or oxygen. However, during this time, they still require some oxygen to live. One of their most fascinating abilities is that they can uptake oxygen from the water around them by absorbing it through their body via special blood vessels. One area of their body that works especially well is their butts!
Curious what frogs do? Many aquatic frogs spend their time on the bottom of lakes and ponds to wait out the winter. However, some terrestrial species such as tree frogs and the wood frog have special “anti-freeze” substances in their bodies, allowing them to survive in shallow soil and leaf litter.
Cloning to survive the winter
Michigan State University Extension recognizes that animals are not the only species that have adapted to cold weather. Some aquatic plants produce hardy clones of themselves called turions (in latin turio means "shoot") or overwintering buds to make it through the winter. These winter buds are densely packed leaves that are often rich in starch and sugars which allows them to act as energy storage structures. When the plants die back, the winter buds will fall to the bottom of lakes and ponds and in the spring grow into new plants. Turions are a nutritious snack for ducks and waterfowl.
A version of this article originally appeared in the February 2023 issue of the Lakefront Lifestyles Magazine.