As reported previously, the sea water micro aquarium is a fascinating system:
though possibly slightly smaller than a real ocean it may still serve as
a perfectly working sea life equilibrium for 12 months or even longer.
All its components are easily available: a toothbrush tumbler, a few soupspoon
portions of fresh, wet sea sand and 100 ml of sea water from the same site.
In addition you might make use of a cover plate (in order to hinder the water from
evaporating, thus preserving its natural salt content) and some spare ocean water, e.g.
kept in a 1 liter plastic bottle. You don't even have to go to the ocean
yourself but instead can ask a friend to pick up a small seasand/water sample for you.
Just tell him or her to use a small plastic film container (from those analogue
films, some of you will remember) and to fill its volume with 2/3 of sand and 1/3
of water. The sand should contain as little bigger organisms as possible (no algae,
no living shells, no fishes and no crocodiles). Instead, some shell fragments and a
slightly coarse sand are welcome - remember that tardigrades would suffocate in fine mud.
Of course the film container should be kept in a dark and rather cool environment
during transport. At home you might place it on a window sill, slightly dark. Sun is
allowed by no means!
At first one might think that such a tootbrush tumbler size aquarium should be
clearly inferior to a big sea water aquarium - but this is wrong. By means of the
micro aquarium in combination with your microscope you will be able to
study many organisms in their infancy - with the advantage of an increased
transparency! As an example you might have a look at the following video clip of
a living baby seashell. Due to the transparency you will be able to look
inside the shell without making use of some more brute human investigation tool, like e.g. a knife.
Note how the shell is moving on the slide. It is feeling uneasy there because
there is an annoying lack of sand. At the end of the clip we present a close-up
which shows how the gills are working in order to pump oxygen into the shell:
The micro aquarium has tremendous advantages: note how
the small shell (1 mm)
is moving and look at the gills in action!
Even though the water volume within the micro aquarium is
rather modest you might be lucky and note true tardigrade population explosions from time to time.
In those cases it is possible to study tardigrade life more easily in detail.
Up to now we had not come across a single picture of of a maritime tardigrade egg in
literature. E.g. Ernst Marcus states that he was not able to find any eggs even in big
tardigrade populations. So we were eagerly looking out for tardigrade eggs as well.
And finally, after man hours of search we came across those colourless empty egg shells
as shown below.
Empty egg shells with the a 'reasonable' diameter (40 µm)
Of course there a many other maritime organisms which are able
to deposit tiny, transparent eggs as well. As a consequence an empty egg shell is not a
fully convincing proof that we have come across a tardigrade egg. So we had to find an
egg with a tardigrade in place.
And in the end we got it!
Though the situation between the sand grains is far from optical paradise you will be able
to note the typical stylet/mouth tube triangle in position 12 o'clock within the egg:
Almost mature Batillipes egg, diameter 40 µm
We were not able to recover this egg from the sand.
But, as we had a very high population of Batillipes dicrocercus within the
micro aquarium at this time (and nothing else) it is highly plausible
that the egg shown above is actually a maritime tardigrade egg. It adheres successfully
to its sand grain - an effective method to avoid contact with one of those
© Text, images and video clips by
Martin Mach (firstname.lastname@example.org).
Water Bear web base is a licensed and revised version of
the German language monthly magazine
Style and grammar amendments by native speakers are warmly welcomed.