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

Sand beaches have the reputation of being a cosy place to relax for the elderly people and for those with small children but at the same time - and for the same reasons - are considered to be void of thrilling or interesting marine life. This was our opinion as well before we began to screen sand samples in search for the tardigrade Batillipes mirus (to be translated as "mysterious shovel foot")
When judged with typical human superficiality ocean sand might be regarded just as a big heap of basically identical tiny sand grains - interesting only for a few specialists, like mineralogists or some of those strange esoteric egocentrics ...
Totally boring, isn't it?

But we had already pointed out in the last issue that this is really a question of scale, of big and small dimension. Already at moderate magnification you will come across bizarre foraminifera housings, jewel like diatoms, interesting fragments of sea urchin stings and many other interesting details.

All those seemingly non-sand-objects are embedded within a colourful micro flora revealing its mysteries only to the patient people among us. There are moments when a simple sand grain appears like one of those fascinating reef aquariums. But, sand collectors be warned, the colourful life within the sand grain is strictly linked to the wet state - when dried most of it will die and vanish. As a consequence further inverstigation might be restricted to the dead remains of the previous "micro reef".

In particular the Baltic Sea, locus typicus of our shovelfoot tardigrade Batillipes mirus , is thought to be less interesting than the "real oceans". Some people even venture to say that it is not a real ocean, when considering its maximum depth of about 100 m and its low salt content - a close to sterile ocean, more or less a freshwater pond with some seasalt added?
Though some of the arguments might be correct the conclusion is wrong. As we have pointed out, a simple dissecting microscope will reveal a tremendous species variety also in the Baltic sea. Just give it a try and have a look at the sand using moderate (up to 30x) magnification.

Sand grain from the Kiel bay, Germany (Kieler Föhrde). Loupe magnification. Diameter ca. 1mm.

Indeed we find many micro organisms, most of them in low individual numbers but with a high variety and a perplexing vividness of colour - standing in strong contrast with the seemingsly uniform sand grain sand colour.

Typical sand grain flora from the Baltic Sea. Micro alga perfectly anchored upon the sand grain surface.

Typical sand grain flora from the Baltic Sea. Colourful algae spreading all over the sand grain surface.

Typical sand grain flora from the Baltic Sea. We do encounter a wide variety of micro organisms here, sometimes difficult do determine the genera, not to speak of the species. Ask your teacher ;-)

After some time we begin to understand what the nature of the tardigrade nutrition might be. not so much the splendid big diatoms with their massive glass housings but the even smaller micro micro algae. So the tardigrade is not "hunting" big diatoms. Instead it is steadily grazing along the sand grain surfaces, like sheep on a meadow thus cleaning our beaches - thank you, tardigrade!

Batillipes trying to clinge to the sand grain surface even though the pathway might turn out to be be strongly curved.

The mouth tube is directed downwards, so Batillipes can move along the sand grain and graze on its surface without bending its head downwards. The stylet action is less dramatic than it might appear - it can help to loosen small algae glued to the sand grain surface. At the same time the head with its multi-sensor equipment will look forward, in direction of the movement.

© 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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