Interstitial live, within the sand in the oceans (II)

What exactly is our maritime Batillipes water bear doing all the time within the ocean's sand grains? Exactly, as with most of us humans, much of its energy is being spent on nutrition management. As you will be able to imagine nutrition might be fairly scarce at a clean beach.

In the micro aquarium: adult Batillipes tardigrade - this time not clinging to a sand grain but trying to change from one sand grain to another. Body length ca. 0.25 mm.

In order to better understand the situation we must have a closer look at the sand itself. Most of us will be inclined to define sand just as a collection of more or less spheroid mineral particles, possibly with nice shades of colour but being void of life.

Just think of those people who are collecting dry sand samples from any touristic location, as a kind of souvenir. Those sand collector have noticed that there are many variations of sand: the colour palette and colour saturation might be extremely variable, as well as the typical grain size and the grain size distribution curve.

A wise observer will note many additional features of those sand varieties: already at the beach it will be possible to perceive additional objects between the sand grains, e.g. really tiny shells and shell fragments and snail housings which would be rated as highly collectible when transferred to our human dimensions. Furthermore you will occasionally come across minute fragments of urchin sticks, fragments of urchin housings, "porcelain" foraminifera housings (some of them looking much alike to a sand grain) etc.

But only when using a 10x loupe or a dissection microscope the tremendous diversity of those innumerable sand objects will become obvious - sand is much more than just a collection of sand grains! In fact it is (depending on the perspective) a cemetery or a specimen treasure of ocean life as well, documenting the beginnings and the mostly sad endings of ocean life:

Sand from Kiel city bay ("Kieler Föhrde") as seen at moderate magnification under a dissection microscope. Note the shell fragments, the stick-like sea urchin sting fragments, the formainifera housings ("glued bubbles") etc.

Because the microscopical search for maritime tardigrades as a rule will take hours and hours, the tardigrade amateur inevitably will become a sand investigator and connoisseur as well. In any case it is worth while to note those fascinating non-tardigrade sand miracles as well. Some sand objects strongly remind of the Fine Arts, e.g. the following Formainifera housing would perfectly fit into a modern sculptures' collection when magnified appropriately:

Foraminifera housing ("deformed and glued bottles") found in a sand sample from the French Atlantic Ocean coast.

Many objects in principal might serve as a potential nutrition for the tardigrades. But many of them, like the worm-egg below are tightly anchored to the grain surface and in addition bear some kind of protective armour in order to repell those nasty hungry micro-eaters living in their neighbourhood.

Tiny worm egg anchored to a sand grain by means of a stick.
Sand sample from the Kiel Bay, Germany.

In the tardigrade literature  diatoms  are named as the typical maritime water bear nutrition source. This is partially wrong and partially right: most of the well-known typical diatoms would be nutrition overkill for our tardigrades and their inner content will not be accessible due to the legendary and apparent strength of the diatom glass housings:

Diatom on a sand grain from a sand sample taken at the Kiel Bay, Germany. Housing diameter ca. 0.2 mm. The attractive inner content is well protected by a solid silicatic (glass) housing.

Diatoms on a sand grain from the Kiel Bay, Germany. Length of the Naviculae ("boats") ca. 0.3 mm. Due to the perfect protection the tardigrades will not be able to feed on those big diatoms.

A microscopical sand survey will reveal that apart from those well protected diatom glass housings much smaller "ocean vegetable" is spread all over the surface of the sand grains. This less splendid, really tiny organic material is the primary nutrition source for our tardigrades. It just has to be found and collected - a task which might be compared to cleaning an aquarium or the walls of a swimming pool by means of a vacuum cleaner. So the menu card of our tardigrades might appear as extremely modest but in fact they are performing an altruistic ecological job by cleaning the sand of our beaches!

We will provide a follow-up to this topic in the next issue.

© 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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