How about those dreadful sea water aquarium constraints?

In the beginning we had been extremely pessimistic with respect to the survival prognosis for our maritime tardigrades within the micro aquaria. As probably all of you will know, sea water aquaria, small aquaria and moreover micro aquaria are generally considered as complicated, inadequate and hopelessly fault-prone. And you don't need much of imagination to understand the big difference: an endless ocean on one hand, a cupful of water on the other - fresh air, wind, waves and currents in the oceans, little exchange whatsoever in a micro aquarium.

Furthermore those sea water aquaria are subject to lots of intellectual discussions based on what appears to be a terrifyingly complicated, physico-chemical background. And we had heard rumours that all those impressive "Sea-life" enterprises were in fact dreadfully dependent on the profound knowledge of their local sea water specialists.

So, when taking a water sample with  Echiniscoides sigismundi  at Lisbon harbour a few years ago we had been eager to note the water temperature and had poured the sample into a thermos bottle at once. We had been convinced that the life expectancy for tardigrades within our small containers might possibly reach only a few days or weeks at best. In order to better care for the tardigrades we planned to control and monitor the salt content of the sea water as well. We thought that similar to a surgeon with his stethoscope we were badly in need for a salt measurement device, a refractometer. Well, today, thanks to Ebay, this was not a great problem and here it is:

Cheap refractometer for salinity measurement.

Refractometer for salinity measurement. Close-up photograph of the glass area (blueish) where the sea water droplet is placed and subsequently quenched down by means of the plastic cover (left) to a small "slice" of water, a very thin layer, for measurement. The next picture shows the reading which you will get from this kind of instrument:

Salinity measurement by means of the refractometer. When looking through the eye-piece at the other end of the instrument you will get the information as shown. In this case we look at low salt content sea water from the Baltic Sea (in German "Ostsee"). On the left side of the display window you will perceive the reading for the specific gravity (Specific Gravity), on the right side the actual salt content is being displayed: 15 per mil.
BTW: The water from the Lisbon harbour contained about twice as much salt as the sample from the Baltic Sea shown here.

So we had become as scientific as possible, being aware of the fact that lots of the physico-chemical informations were still unknown to us: exact chemical composition of the salt, organic matter content, pH, electrical conductivity and so on. In any case we kept the sea water aquaria with the tardigrades in low-light condition, on a cool window-sill facing no sunlight at all. In order to keep evaporation as low as possible (to keep the salt content constant), there was always some kind of cover on the micro containers.

Funny enough, the tardigrades made clear that they didn't care so much about the exact physico-chemical condition of the water. And apparently they didn't severely miss the rest of the ocean as well (we think so at least). In the end it turned out that all our "scientific" precautions had not been necessary. The tardigrades tediously kept on living in the micro aquaria for 9 months and more. Lots of tardigrade youngsters proved that life did in fact continue without noticeable problems.

But all of us know that we are on earth, not in paradise. After those nine happy months we noted changes in our favourite aquarium. Green algae took over, very slowly but steadily, starting with a slight green hue at the beginning and apparently covering all surface areas after some weeks. Most of the inhabitants of the micro aquarium (acarinae, nematodes, ostracoda, ciliata) were able to cope with the new situation. But we were sad to note that our tardigrades didn't survive the green coming-into-power. Next time we will take care to have strongly subdued light.

Increasing amounts of green algae take over the micro aquarium, starting from the white calcite particles as shown in the picture (the photograph shows a big calcite particle, a few mm in width, with an unidentified, chemically different white particle on it).

So, overall, we have learnt a lot from this tiny experiment and we hand the result over to you in order that you will be actually able to take profit from it.

(1) Passive (self-preserving) micro sea water aquaria are perfectly possibly and they can serve as long lasting sources for the study and admiration of the marvels of nature.
(2) You will really be able to come across a lot of adventures (when comparing e.g. with typical touristic travel)
(3) Sea tardigrades kan be kept alive in a micro aquarium for at least 9 months
(4) The micro aquarium might be an ideal source of study for education in schools
(5) No chemistry and no special eqipment needed
(6) No feeding and therefore no cleaning needed (the tardigrades feed on micro algae)
(7) Even a small photographic film container might do the job

Optimum results seem to be favoured when sticking to the following rules
(1) Use a slightly bigger container if possible, fill in a few mm of sand, and keep the water layer above at about 5 mm depth
(2) Take care that there are no bigger organisms in the sample (basically only sand grains and shell gravel)
(3) Keep the aquarium covered by some kind of glass plate, petri dish etc.
(4) Make sure that no sun light at all will reach the aquarium and keep it rather cool (light ~100 Lux, temperature in a band beetwen ~ 16 - 20°C, depending on the local condition of the water source where you took the sample)

Just do it!

© 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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