|A DETACHABLE-NECK FLASK TECHNIQUE TO SAMPLE MICROINVERTEBRATES FROM FINE GRAINED SUBSTRATA.|
Key words: New sampler, sampling, micro invertebrates, detritus.
All the technical terms displayed in yellow are explained in the Glossary. It could be a good idea to pay an initial visit to it.
Most microscopists gather their aquatic samples of organic sediments from the bottom (benthos) or from materials adhering to submerged objects (bioderms), or to rooted or floating plants, (periphyton). Normally they are small samples.
The examination of those samples is done in the laboratory, taking drops with pipettes from different parts of the collection. So chance plays a most important part in the amateur’s findings; and the time that it takes to examine each sample causes it to deteriorate and only a few of the many present species can be detected.
specialists in diverse branches of the zoology of micro invertebrates,
mainly the ecologists, use, whenever they can, harvesting methods that
concentrate in small volumes the microfauna of great volumes of the
The typical example is the
plankton net which
collects in a small container the living beings existing in the water
column by straining when it is dragged through.
specialists in edaphology, for example,
they want to gather soil nematodes, use a Baermann
funnel; the soil micro-entomologists use the Berlese-Tullgren
to separate acarii and other groups of
micro-arthropods from litter or soil.
instrument that I will present in a professional version in
and in an "amateur’s" one here, performs a similar task with micro-invertebrates, which
are abundant in fine
bottom sediments (ooze)
or in filamentous algae
floating or fixed to some substrate (plocon and
heteroplocon) or in the periphyton
that surrounds the stems and leaves of
rooted plants, submerged or emergent, in the different water bodies (bafon), or in sediments that
the floating plants (pleuston)
catch between their roots.
In all those cases the sample is an abundant collection of organic microparticles grouped in floccules, between which the micro-invertebrates move and hide themselves. It is very frustrating while examining at the microscope our drop of sample to see that the micro-invertebrate of interest, after some fast movements in free solution, that whet up our curiosity, subsequently hide up and disappear for long minutes behind a floccule of detritus. This is for example an irritating and common behavior of Gastrotrichs and Catenulida.
rotifers, gastrotrichs, nemertines, turbellaria, entomostracans
and ostracoda), nematodes, microoligochaeta (naidids and enchytreids)
and freshwater mites can be represented in the samples. (Try their
browser's search engine to find a definition of those terms you don’t
know). The sample won't reveal information of
the first developmental stages of the larvae of many insects, that also
in the same habitats.
to separate the organisms from the sediment, and to concentrate them in
volume of clean water, which can be easily screened out, I have
of transparent plastic of about 7 to 10 cm in length, and a diameter
the neck of the bottle is adapted to it so that it fits tightly,
allowing any loss of water. It is possible to complete the adjustment
the end of the tube with one or two turns of plastic electrician's
adhesive tape is not as efficient for this task. Hypodermic syringes
with their ends cut away can make excellent samplers. You can wipe the
scale off with
Obtaining a watertight closing is possibly the more difficult step for the amateur. The bottle and the added tube, totally full of water, must not lose liquid over several hours. The tube fit does not have to extend beyond the neck of the bottle, so that the micro-invertebrates can easily find their way up. In addition it must be easily removed to examine its content.
this simple system is built and used, the removable tube must be pulled
a rubber stopper is placed in the interior of the bottle fixed to the
end of a rigid wire, preferably stainless steel
or copper, that exceeds conveniently the length of the assembled
a shaft of not less than a millimeter
in diameter to allow an easy manipulation (the wire I used for the
the only stainless steel one I could find, but is too thin). [David
Walker suggested the thinner style of wire clothes hanger when straightened and this should work fine]. The
of a diameter that exactly closes the lower end of the separable
tube, and must be soft, to adapt itself easily.
to use this instrument, it is filled to approximately one third or one
its volume with detritus, or filamentous algae, or vegetable roots, or
suitable materials. The cork is placed in the interior and the sampler
assembled sliding the tube down the shaft and fitting it to the neck.
instrument is now totally filled to near the end of the chimney with water
from the sampling place, it is
placed in a well lit site (or it is illuminated with a desk lamp in
laboratory) and it is left to rest for 3 or 4 hours.
Using the rigid handle, the stopper is raised, and it will close the lower end of the tube. Once ensured that it is closed, and firmly holding the shaft with your thumb and index finger, the tube must be removed with care, and emptied into a container of suitable volume.
Now the tube can be opened and with one washing bottle filled with water from the same source as the sample, the walls must be flooded to release the organisms that could be adherent to the walls.
Reassemble the sampler, fill up the tube with water, and start a new cycle. The procedure can be repeated for 6 to 12 or more hours.
An Erlenmeyer flask of 250 or 125 milliliters with a TS 24/40 ground neck is fitted with an inner TS ground joint of the same size. The tube of the joint must be cut to a length of 70-75 mm up from the ground portion. When it is desired, the chimney thus constructed can be closed by means of a Nº 6 or 7 rubber stopper, fitted to its lower hole. The stopper, minor diameter upwards, is fixed to a copper or stainless steel wire rigid shaft, with a diameter of 2 or 2.5 mm, and a convenient length.
The sediments and other materials to examine can be pre-concentrated and sorted by size, sieving them through a graded series of ASTM standard sieves. Sieving can be avoided, but this treatment provides in most of the cases a cleaner and more abundant collection.
An additional advantage of size sorting the sediments, is that it allows a coarse separation of taxonomic groups, which can require different preservation methods, giving the opportunity for a more individualized treatment.
The instrument was designed in 1976 to help collect the inhabitants of the rhizosphere of tropical floating plants (pleuston) of a great variety of kinds and sizes (Azolla, Pistia, Eicchornia, Salvinia, etc.) but it was also useful in the treatment of ooze samples from an ox-bow lake whose bottom is formed to a large extent by vegetal detritus, and fine clay.
a. Taxism: oriented (positive or negative) movement (displacement) of an organism in response to an outer stimulus, light, gravity, etc. i.e. the protozoa show positive quimiotaxis when they are accumulated next to a drop of air under the cover slide.
of a generally sessile organism (a plant by example) in response to an
stimulus. i.e: the roots show positive geotropism, the stem negative
c. Aerobes.- organisms that they need oxygen to breathe. Those that don’t need it are denominated "anaerobes".
d. Axenic cultures.- they are monospecific cultures using a media designed to provide species with all the chemical nutrients they need, without use of live food. Several species of protozoa (and also other micro-invertebrates) can be cultivated by this technique.
e. Baermann’s funnel. A funnel, almost full of water, with a sieve where the sample is placed, and a rubber tube on the end of its tip, closed by a valve or clamp, very useful to gather nematodes from the edaphon, or finely chopped vegetal tissues. In addition to the soil nematodes it is common to gather also microoligochaeta.
f. Berlese-Tullgren funnel.- A funnel similar to the previous one, but whose tip is placed over a tube or bottle with alcohol, and in whose sieve are placed samples of soil or litter. A lamp warms up swiftly the surface of the sample and as this dries up the micro-invertebrates go down and they finish falling into the alcohol.
g. Benthos.- bottom materials, with the inhabiting organisms.
h. Bioderm. Any set of microscopic live beings, animals, algae, fungi, bacteria, which grow on a live or inanimate firm surface. Almost a synonym of periphyton, but these are a bioderm on plants.
i. Diversity.- A sample composed by a single or a few species is a "uniform", or "little diverse" one. When one sample has many species it is a sample with great "diversity". They has been designed mathematical indices to measure that diversity based on the proportions of the diverse species that compose the sample.
j. Edaphology.- science that studies the soil. The set of animals, fungi, bacteria and algae that lives in this habitat is denominate "edaphon".
k. Heteroplocon. It is plocon loose, and originally or secondarily floating.
l. Monospecific cultures or polyspecific cultures. It is possible to make rather easily “polyspecific cultures” of micro-invertebrates, in which several species grow up together, normally on a mixture of foods, or preying one on the other. Cultures with only a single species ("monospecific") are more difficult to establish. In this type of culture one selected organism is grown mixed with an appropriate prey. For example: one protozoan with food bacteria.
m. Ooze. It is the organic detritus sediment layer, which is deposited on the surface of the bottom of the water bodies. This layer is inhabited by a multitude of organisms that form a chain of decomposers of the organic components of the detritus.
n. Periphyton.- Layer of bioderm, adhered to the submerged parts of plants (stems, leaves).
o. Pleuston.- The free floating plants with the animals, algae and bacteria that inhabit them, be they in their leaves, or especially on and between the pending roots of the same ones.
p. Plocon.- filamentous seaweeds adhered to an alive or inanimate substrate, with the microscopic beings that live on or among them.
q. Qualitative sample. It is that in which only the kinds of elements that compose it, not its amounts or proportions, are of interest.
r. Richness. Is the number of species that are present in the sample.
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