Surviving the frost: the hidden lives of fish and organisms beneath icy lakes

Lake living can be challenging at the best of times, but with winter comes another hurdle: ice. As the surface of lakes freezes, light and oxygen suddenly become much more limited. That could be a potential threat, but luckily organisms that live in lakes have come up with some cool ways to survive.

Metabolic changes

It turns out that fish are a bit like us when it comes to the winter months; they become less active. That’s because they are cold-blooded (not like us), meaning their metabolism slows down when the lake temperature drops.

They are also helped by the layer of ice on the surface which provides some insulation. The resulting relatively warmer water beneath the ice is compact and thus sinks to the bottom of the lake, where the fish then huddle together and cool off for the winter. Certain species, such as koi and gobies, have the ability to burrow into soft sediments and enter a dormant state. During this time, their heart rate drops, they don’t need as much food and oxygen, and they don’t exercise much.

Plenty of other creatures beyond the water use similar tricks to survive the winter as well. That’s why you should probably bring a helmet if you go to Florida in the colder months, just in case there are sleepy, falling iguanas.

Built-in antifreeze

A frozen lake is home to much more than just fish, and it’s undoubtedly the insects that live there that have the coolest methods of surviving the bitter temperatures.

Some insects have a kind of antifreeze in their cells. Like nature’s equivalent of the strong-smelling canned stuff you spray on your windshield, this cryoprotectant is made from specialized carbohydrates that lower the freezing point of their bodily fluids. This prevents the formation of ice crystals, which could otherwise burst the insect’s cells, leading to fatal damage.

Other insects, however, just suck it up when it freezes and have adapted to let the ice crystals do their thing. Insects that live in the lake, such as dragonfly larvae and water skippers, produce proteins that help control the freezing process, known as ice nucleators. This helps prevent the ice crystals from damaging their cells by essentially freeze-drying them.

Should lakes freeze?

For quite a few lakes, the freezing over is all part of a larger, crucial process. Known as lake turnover, the water in the lake literally rotates from top to bottom, with the surface layer being hottest in summer and coldest in winter. This process is important for the distribution of oxygen throughout the lake waters, allowing respiration and organisms to survive.

That is why it is also important that lakes melt and the turnover process continues. Once sealed off by ice, the situation becomes something like a plot point found in many clichéd survival films: there is suddenly a finite amount of oxygen and it is gradually running out.

Lakes can contain phytoplankton (albeit at lower levels in winter), which normally take in carbon dioxide and produce oxygen through photosynthesis, but this requires light, which is also quite scarce. If the lake remains frozen for too long, organisms will begin to die from a lack of oxygen. Even if they have adapted to use less of it, like fish, they still need some amount to live.

Lack of oxygen can also occasionally lead to ‘winterkill’ in smaller frozen lakes. As plant life dies, what little oxygen remains can lead to decomposition, which further decreases oxygen and, as a result, kills even more organisms.

With global warming this may not be a problem; many lakes are melting sooner than ever and some are not freezing at all. That may sound positive for the residents of the lakes, but it can disrupt the delicately balanced turnover process, and with it the oxygen and nutrients they need to survive.

All “explainer” articles are confirmed by fact checkers to be correct at the time of publication. Text, images and links can be edited, deleted or added at a later time to keep the information current.

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