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A small microfauna sediment sampler

Walter Dioni                                                           Cancún, México

A friend, thinking that it could be helpful for my researches, informed me of a small device of which he has had news, although he can’t remember the source of the data. It turns out to be, functionally, very similar to my "Detachable-Neck Flask" sampler.

(http://www.microscopy-uk.org.uk/mag/artmar05/wdextractor.html)

I made a long and difficult search (because I didn’t know what the appropriate key words could be) but I found no one reference online.

But it's really useful, so I publish it, hoping that it serves others and, in addition, that someone can get an idea of who is the original author.

I report here the procedures that were reported to me, but it is easy to see that these can be adapted to the needs of everyone. In a test tube, 17 mm internal diameter by about 15 cm high, 2 cm of sediment were placed at the bottom. Add water (preferably from the sampling site) to 4 cm of the upper rim. And then slip inside, along the tube wall, another small tube 5 cm long with an outer diameter of 15 mm.

Injecting water into the small tube (a dropper, or a hypodermic syringe could be adequate) it sinks until its content reaches the outside water level. A meniscus of water, whose greatest width is only 2 mm is so delimited. After 1 or 2 hours and for the next 24 hours the micro-fauna which rises to the surface could be sampled, taking drops with a pipette. Of course, the water level drops by evaporation (if not limited and controlled using a humidity chamber) and by the withdrawal of samples itself. To maintain a suitable level of the meniscus, inject into the small tube a few drops of extra water. While the tube sinks, the outside water level will rise automatically. Simple, efficient and elegant don’t you think?

To the right is a schematic version of the instrument. The water is shown somewhat below the optimal level of work.

In the following illustration (a version which my grandson Axel Quarchioni prepared in C4D) a suggested working assembly is displayed.

I didn’t receive instructions about this, but it seems logical to prepare an opaque cardboard cylindrical sleeve, such as that shown in the figure, to shield the sampler, leaving exposed only the top of the water column to stimulate phototactic responses.

Of course dimensions are not critical. The really important thing is to maintain a thin meniscus, but one that supports the sampling with pipettes.

As in the detachable neck sampler, the collected micro-fauna will be those organisms which are phototactic positive, geotactic negative, aerobic, and sensitive to the acidity of the medium. I imagine that, as in my instrument, the majority of the tigmotactic and geotactic negative fauna will die in the sediment**.

The advantage of this little, smart system, lies in the very small sample volumes that can be processed, which in many cases is all that is available (think of small ponds, tree holes, abandoned automobile tires, open tin cans exposed to the weather, stagnant pools of rainwater from bromeliads, periphyton scrapings, small collections of filamentous algae, etc).

I know of only one reader who has built one professional version of my detachable-neck flask sampler. If someone else has done experiments with that system, or tries this tiny version, I am interested in feedback and results.

** A suggestion, that perhaps could work, would be to put over the sediment a relatively thin disk (4or 5 mm) of medium or large pore polystyrene foam*, and then assemble the instrument. The smallest and most mobile micro-fauna should cross the barrier to gather at the surface. Tigmotactic species would invade the new material, and could be sampled by removing and washing the sponge in clean water in a small capsule, at the end of the surface sampling time.

* This type of sponge is common in Mexico, as it is used in medication bottles to prevent the destructive movement of tablets. Any piece of plastic foam of similar size could serve.