Imagine creatures which can survive years of freezing, days of ultra-high temperatures, living in a vacuum or extremely high pressure, and even exposure to radiation thousands of times the amount that which would instantly kill a human. Why, these would seem to be abilities only conceivable in some science fiction extraterrestrial. But all around the world, from the bottom of the sea to the highest mountains, from the Poles to the Equator— and even reportedly experimentally in outer space— hundreds of types of such extreme creatures do exist.
These are the extremely small animals called water bears or members of the Phylum Tardigrada. They have bodies that are segmented, so they are often considered somehow related to certain worms. But then again, because of other features, they are also said to be allied with arthropods. While not really coming to any agreement in this regard may be hard to come by, almost all agree that water bears are amazing— and quite strange.
Tardigrades are considered to be a very old grouping, with suspected remains being discovered in Cambrian era amber. Even though they did not come to the attention of science until the late eighteenth century, they are now known to inhabit just about every environment, from fresh and saltwater (as their common name implies), and even dry land. They generally like to eat plants and bacteria, but some appear to be predaceous.
There are probably about 750 species of tardigrades, but none of these are very easy to see with the naked eye. The biggest of the big water bear reaches only 1.5 mm in length (with the small ones less than 0.1 mm when fully grown). With some species, though, they make up for their small size by staggering large numbers; for example, over two million in a square yard of moss.
If a person is able to get enough magnification to be able to get a good look at one of these minute critters, their quaint common name almost makes sense. They are fairly pudgy in appearance, with notable, nasty looking claws on their chubby legs. They have eight legs rather than four limbs of a true bear, and they don’t have any fur, but only a few dangling filaments and cirri— close enough when it comes to namesakes. (Same can be said in regard to their other quite picturesque common name— moss piglet.) And while true bears deep-sleep, and not really hibernate, when things turn cold, water bears are hyper-hibernators, being able to shut down entirely when exposed to freezing conditions (there are an assortment of terms for their latent states, but they all serve the same function of complete shut-down).
The most famous beach-baby water bear is the cosmopolitan Tidal Water Bear (Echiniscoides sigismundi). It is one of those species that seems perfectly happy scooting between grains of sand of the upper tidal zone, but it also has a preference for green alga Enteromorpha and also the cracks and crevices of certain types of barnacles. And since such seaweed and barnacles often grow on boats and ships, and these vessels often will plow the seas, the exact status of this tardigrade in any given location is hard to determine. It potentially could be native— or it could be just a hitchhiker who came along for the ride as part of the fouling ecology of the bottom of a boat. Such long-distance sea travel would certainly be possible for the Tidal Water Bear – it can ‘hold its breath’ or survive up to six-months submerged in the sea, plus it can go about the same length of time frozen (which can potentially be very useful in the some of arctic areas it is found). Or it can manage in completely pure rainwater (useful when in the high tide zone) and there has been one record of it being found over a half-mile up a mountain in Africa.
Two species of Batillipes water bears have been reported along California beaches – B. gilmartini and B. mirus. Member of this genus don’t have bear-like claws but have suction disks on the end of the legs. It is theorized that this allows the little tardigrades to zip about on grains of sand in a fashion similar to a gecko scaling a wall.
Styraconys sargassi is also known from the West Coast. As its name implies, it was originally described from the pelagic sargassum seaweed, but certainly there should be more than enough rich kelp growth offshore of California to keep this little water bear happy.
Not that tardigrades seem that hard to please. With their extreme tolerance of extreme conditions, they really are wonder beasts of whatever environment on earth— or experimentally beyond— that they may be found. After all, water bears seem to know the secret of survival when things get really tough. They will simply go to sleep and wait for the danger to pass.
