A rock wall (II) - or: holiday time

The previous magazine had been dedicated to a small rock wall in Austria. We had come across it when walking from the small town of Abtenau to the so-called "Rocheralm". As the upper heights of the rock wall were difficult to access we had simply collected a few moss samples that had fallen down to the ground. As those moss samples can be considered as fairly typical we would like to use them in order to illustrate the procedure and to show what you can expect to find in a good moss sample.

One of fallen moss cushions was fairly big. We separated a small part of it for our tardigrade search (the balance showing 0.72 g), That's what it looked like:

Fraction of the "fallen moss" (0.72g) in the Petri dish, before adding water.
The ruler on the right is indicating [cm].

The wetting procedure is best performed with good quality (chlorine-free) tap water, alternatively with clean rain water or low ion content mineral (non-sparkling!) water. A perfectly dry moss like the one shown will soak much water during the first minutes. Add some additional water in order to keep the water level at about 3 to 5 mm.

The same moss during the wetting process

After at least 4 hours of soaking we remove the moss (just parking it in a second Petri dish) and investigate the water and debris residue which has remained in the dish. Take care to remove any remaining soil as it might consume too much oxygen thus annoying or even suffocating the tardigrades. If the tardgrades in the Petri dish do not move after 4 hours of soaking something has gone wrong.

Residue in the Petri dish after the removal of the moss

The most promising optical device for finding the tardigrades in the Petri dish is a dissecting microscope (synonym: stereo microscope). Those instruments are characterised by a rather low magnification in combination with a two-eyepieces' steroscopic view. For our purposes a magnification between 20x and 30x should be chosen, not more and not less. Use incident (cold!) light like LED light and a black background. You will come across other members of the moss microfauna like this nematode shown below which normally should be moving vigorously:

A nematode from the rock wall sample (in the very center of the photograph), as seen under the dissecting microscope using incident light. Image width ca. 6 mm.

The same nematode in typical movement, at higher magnification. Image width ca. 0.5 mm.

Normally those moss samples will contain some rotifers as well. The rotifers move in a different manner (stretching and contracting) and they have a just a single leg, whereas the tardigrades have eight legs.

Rotifer as seen under the dissecting microscope (center-right, position 4 o'clock). As long as the rotifer feels comfortable, it tends to shovel particles into its stomach by means of its "wheels". These are no wheels of course, just moving ciliae, but they definitely look like wheels.
Image width ca. 6 mm.

At higher magnification in the classical microscope we can get a clearer image of the wheels. Besides we can see that the rotifers have vertical striae. This is different from the tardigrades (which have segemented bodies, resulting in horizontal striae). Image width less than 0.5 mm.

When counting the microfauna members from this 0.72 g sample we found the following:
-- ca. 25 rotifers
-- a few nematodes
-- 6 Eutardigrade water bears
-- 2 Echiniscus water bears
When comparing with Ernst Marcus' reported maximum tardigrade population count of 22,000 individuals per gramm moss this finding might sound not very impressive. But it is quite typical. Moreover, the follow-up investigations revealed that the moss cushion is by no means boring, in fact showing an interesting mix population of several tardigrade species. On the other hand it becomes clear that it is not easy to choose the appropriate moss sample size for soaking. 22.000 individuals whould have been to much - but the 8 tardigrades found in our sample might be too few to be representative.

We begin our series of portraits from the rock wall inhabitants with the carnivore Milnesium tardigradum:

Milnesium tardigradum from the rock wall sample. The broad buccal tube allows carnivore behaviour - i.e. eating of smaller animals as a whole! Image width ca. 0.3 mm.

We will have a closer look at some other tardigrades from this sample in the next issues of the magazine. See you!

© Text, images and video clips by  Martin Mach  (webmaster@baertierchen.de).
Water Bear web base is a licensed and revised version of the German language monthly magazine  Bärtierchen-Journal . Style and grammar amendments by native speakers are warmly welcomed.

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