We are only just discovering megafauna species at the very bottom of our oceans, let alone have a good understand on what a Tardigrade is. Their phenotype resembles the photo below (Figure 1). They are often referred to as ‘water bears’, and as the name suggests, it is because they move similarly to that of a bear and they inhabit the Arctic Ocean, but are also found in a wide variety of habitats. These organisms are phenomenal, they are categorised under a group called ‘extremophiles’.

A conceptual model of what a Tardigrade looks like. (Source- Schokraie et al., 2012)

The type of habitat they thrive in is often considered inhabitable or extreme environments, but the key point here is the need to remember that just because a certain type of habitat may be unfavoured by one organism, does not mean that it cannot be the ideal environment for another. This is exactly the case for the Tardigrades.

One of the most interesting things about these creatures is that they can survive in almost any habitat, from sub-zero temperatures to extremely low saline waters, and even areas where there is large changes in pressure! Tardigrades tend to slow down their metabolism completely in order to cope, or adapt, to live in such harsh conditions. Such conditions that will be focused on in this article, is sub-zero temperatures and extreme heat.

Living life to the extreme – below freezing and being super-heated.

Tardigrades are not a force to be reckoned with. It is has been found that they have a fossil record dating back to around 530 million years ago. You can heat them up, freeze them, crush them, and desiccate them and they would still thrive under these conditions.

One scientist in particular, Gilbert Rahm, once heated a select number of Tardigrades to a temperature of 151°C. Surprisingly, the rate of mortality was not 100%, after the experiment was carried out. Tardigrades curl up into a ‘tun’ which is more scientifically known as a anhydrobiotic state, which is an animals physiological response to a drastic change in environmental conditions. However, these creatures take it one step further, they are able to dehydrate and rehydrate themselves in order to survive in their tun state (Figure 2). Having this unique adaptation does come with one major drawback, they become dormant, and this leaves them incredibly vulnerable to being predated on and any threats that may be present in their environment.

Figure 2: A Tardigrade displaying desiccation and rehydration.

Apart from being left vulnerable in this state, they have to cope with the extremely cold temperatures.  It is not unheard of to see some animals, including fish producing antifreeze proteins, which lowers the point at which ice will form in their cells. Basically, allowing them to survive much lower temperatures than other organisms. To this day, these antifreeze proteins have not be detected in a single Tardigrade species. So how do they do it?

Well, a Tardigrade’s body is composed of ~85% water and it is fact that when water freezes, it expands, meaning that this organism would start to expand and possibly burst in sub-zero temperatures. Tardigrades use their unique ability that allows them dispose of at least 82% water, leaving them with a 3% water content. They start to desiccate themselves or display their ‘tun’ state, so there isn’t enough water within the body for it to expand, thus allowing them to thrive in harsh, polar conditions.

Beyond our orbit

Their common name, the ‘water bear’ suggests that Tardigrades are found in the ocean and even possibly on land, but now there are reports of them surviving in space. A group of Russian scientists were doing their routine analysis of the International Space Station (ISS). They expected to find the usual contaminants from the engines that you expect to see during a spacecraft flight, instead finding a group of planktonic organisms clinging to the side of the ISS.

It has taken the human race an incredibly long time developing the correct type of equipment in order for humans to survive in space. It is a well known fact that if you venture out in to space without protection, you’ll die. The amount of pressure, or lack there of, forces air from the lungs, gases in bodily fluids start to expand causing the human body to inflate. Eardrums would burst, and your blood can even boil as your capillaries being to rupture, without the right gear. All of these bodily changes can render you unconscious in about 15 seconds. The conditions (i.e. Pressure and lack of oxygen) in the atmosphere of space is a harsh reality for people, but Tardigrades seem to survive here.

This then kick-started a large amount of interest; how on Earth did these organisms survive 204 miles above the planet’s atmosphere? In 2007, these creatures had their limits tested. Tardigrades in their anhydrobiotic state were attached to a satellite and launched into space. The results observed were that of, well, quite astronomical. It was found that these creatures had no problem surviving the harsh UV radiation that space has to offer, baring in mind that the UV light is 1000 times stronger than it is on Earth.  It was also found that even in this perfect vacuum, they were able to produce multiple embryos that contained viable offspring, and when hatched out were perfectly healthy.

Will they be here after we have gone?

Absolutely. Tardigrades were possibly even here before the dinosaurs were, so there is no doubt that their chance of surviving long after the human race goes extinct, is pretty high. They are often referred to as ‘virtually indestructible’ and they don’t hold that title lightly. They are able to withstand a whole decade without food, and can even thrive without seeing a single drop of water within this period too. The human race does not even compare to that, whilst only being capable of starvation for about a month. Being at the top of the food chain really is not all that it is cut out to be.


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