Tardigrades from a supermarket!

External contribution by Marien-Gymnasium, Werl, Germany

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Annotation: We are glad to present a third-party experiment here once more. The copyright owners of the text and the images are the pupils Nika, Luca and their teacher Marco Hagedorn from Marien-Gymnasium, Werl, Germany.
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As our readers do know tardigrades are settling in very diverse habitats. As far as terrestrial tardigrades are concerned, many of them are living in minute traces or thin layers of water. Until now the articles in our magazine covered interstitial tardigrades living in mosses, lichens, ocean sediment and soil.
A much more special, soil-like environment can be found in supermarkets, even though the hygienic standards of those markets nowadays are high. Minute soil residues on beet and horseredish are no surprise and shouldn't be regarded as blemishes of the merchandise. Moreover the customers nowadays tend to prefer vegetables in a less perfectly cleaned state which is commonly considered as more "natural" - in contrast to "industrial" food. (fig. 2).

Fig. 1: Horsereddish and red beet with minute soil residues

Fig. 2: A new trend - potatoes which are declared as intentionally less cleaned

Nika (school class 6) and Luca (class 7) investigated this topic within their "Jugend forscht" (youngsters performing science) activity. For this endeavour they soaked supermarket vegetables for three hours in cold, oxygen-rich water. This time span should suffice for typical tardigrades in the dry state (so-called "tuns") to perform rehydration. After the soaking process the vegetables were softly scrubbed with a brush and the water passed through a sieve of 20 µm mesh width. The usual search in a petri dish under the stereo microscope followed. And indeed, tardigrades could be found in two of three studied vegetable species! But even though the procedure was soft the tardigrades didn't move actively afterwards but a species determination could be performed nevertheless.

Please have a look at the results:
On beets Ramazzottius oberhaeuseri tardigrades were found, one of which was plagued by an ektoparasite (fig. 3). Besides, there is no reason to assume that those highly specialized parasites might represent a potential threat for Homo sapiens vegetable consumers.

Fig. 3: Ramazzottius oberhaeuseri on red beet

Fig. 4: Ramazzottius oberhaeuseri on red beet, with parasite

Hypsibius convergens tardigrades were found to live on potatoes (fig. 5).

Fig. 5: Tardigrade from a potatoe

No tardigrades could be found on horsereddish. Possibly horsereddish tastes simply to hot for our eight-legged friends? As we know plant genera have developed many strategies in order to defend themselves against avid enemies during the course of their evolution, so this might be one them.

Summary
Minute residues of soil on supermarket vegetables can definitely contain tardigrades. It is fascinating to note that they are by no mean rare on those vegetables. Further studies in this field are planned by Marien-Gymnasium Werl in the near future.

© Text, images and video clips by  Martin Mach  (webmaster@baertierchen.de).
The 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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