Be warned! Christmas is quite close, there is no way out. In order to cope with the urgent and increasingly exotic gift demands of your environment you might consider an elegant escape: the brand new December issue of the Swiss nature magazine "La Salamandre" is dedicated especially to tardigrades. Feel free to use the direct  order link  now ("Commander ce numéro"). You will be able to browse through a preview version of the tardigrade issue on-line as well.

There is also a nice tardigrades kids' edition available with the title "SUPERTARDIGRADE!" - sorry Superman but you are second with respect to survival capabilities ...

Maritime Tardigrades (II)

"How to search and, more important, how to actually find them?" - these will be the vital questions once you are going to focus your interest on marine and maritime tardigrades. Of course, all of us have a rough idea about the object (some tiny animal crawling about on eight legs ...) and a rough idea where to look for it. For a start any beach along the borderlines of our continents or marine islands will do. Methodology needs to be considered, too.

Please allow a short flashback to the roots of western civilisation which underlines the importance of the right equipment when doing a research:

Rewarding objects of desire? Where to find? How to approach?
Optical tools have always been welcome in the history of mankind
when trying to get hold of some target. 18th century French engraving.

Before starting off to the seaside, we suggest to have a glance at the respective scientific literature. As we had mentioned in the last magazine, e.g. the French zoology professor Felix Dujardin obviously had found just a single maritime tardigrade individuum all over his life. Also the German professor Ferdinand Richters needed extensive microscope sample screening time ("weeks") in order to collect enough specimens for his  Batillipes mirus  publication.

The big advantage for ourselves who are later in history is that we can rely on dozens of maritime tardigrades' hunting reports and many, many scientific articles in order to better estimate the potential chances of planned seaside expeditions.

E.g. Hartmut Greven in his tardigrade book quotes some work performed by Schmidt (1969) who collected Batillipes tardigrades from a beach at a German island called Sylt (better known as a fancy holiday resort for the ultra-rich). He collected sand samples from depths between 10 cm and 50 cm and counted individuum numbers of 300 tardigrades per 50 cm³ at most. This means at maximum  six tardigrades per cubic centimeter of sand - not alltoo much.

Claude Delamare Deboutteville whom we like to quote not only because of the glamorous sound of his name published an ample monograph exclusively dedicated to interstitial littoral sealife. In this book he mentions a publication by Pennak (1939) who took 10 cm³ samples of sea sand, ca. 150 cm inland from the shoreline and who found individuum numbers as listed below:

Genus

Individuum no.

Bacteria

4,000,000

Protozoa

400

Copepoda

40

Tardigrada

20

So it is evident that Pennak found only two tardigrades per cm³ of sand.

Susanna de Zio (1966) reports maximum tardigrade counts of 161 individuums per 3 cm³ of sand, typical averages ranging between 0 and 30, thus documenting typical population densities of 10 tardigrades per cubic centimeter of sand at most.

So we shouldn't be too optimistic at the very beginning: when screening sand in a Petri dish we will be able to look at a quantity of about 0.3 g of sand and typically should not find more than one or a few tardigrades at best. This is the reason why we do have so many collecting recipees in literature. But, to gain a more positive view, you can bet that there will be quite a few tardigrades out there nevertheless. And in any case there is plenty of sand available for you to screen at a typical beach ;-)

Sand beach at the French Atlantic Coast, north of Royan with many, many tardigrades, distributed among even more sand grains ...

Okay, we have been digging at a few beaches. The crime scene looks terribly at the moment but it will perfectly vanish after the next high tide:

Tardigrade digging at the French Atlantic Coast, south of Royan.
On the left side: a toothbrush plastic container for water specimen collection. Please be careful not to loose any glass equipment at the beaches - children and grown-up people later on might step into glass residues and become secondary victims of your research activities!

Of course we have tried some of those many collecting and enriching recipees from the literature: filtering, immersion and decanting, driving out the tardigrades by means of melting sea water ice, by magnesium chloride solution etc. but in the end we came to the conclusion that the simple collection technique by means of shoveling sand with a plastic film container is the best suited method for the beginner.

In our opinion the very best tool for maritime tardigrade collecting: a film container (you will remember, we used those in the analogue photography era).

The best results were achieved when collecting samples at low tide, very close to the water borderline. Simply take some wet sand, add a little bit of sea water, keep closed and make sure that it will stay below 20°C all the time. Be careful to completely avoid bigger animals and decaying plants in the film container.

Even when screening those samples with a very good dissecting microscope at 30x magnification the tardigrades are difficult to find. The following photomicrograph is intended to demonstrate the size relation with respect to fine sand grains:

The micrometer scale (top left) measures 0.25 mm, so the tardigrade body length is well below 0.1 mm! Note that even fine sand grains (appearing black in this case) look like rocks when compared to the tardigrade body size.

How did we notice our first maritime tardigrades? First of all because of those magically moving sand grains like the white one below:

Don't worry, better videos will follow in the upcoming issues of our magazine. This issue was just intended to point out that the study of terrestrian tardigrades definitely will be more easy-going for the beginner.

Literature

Hartmut Greven: Die Bärtierchen. p. 65. Wittenberg Lutherstadt 1980.

Claude Delamare Deboutteville: Biologie des eaux souterraines littorales et continentales. p. 86. Paris 1960.

Susanna de Zio und Piero Grimaldi: Ecological Aspects of Tardigrada Distribution in South Adriatic Beaches. Veröffentlichungen des Instituts für Meeresforschung in Bremerhaven.
Special Volume II (1966) p. 87-94.

© 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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