Looking at green slime and hay infusions

A note: the microscopy material that I am putting in this blog at the moment was originally written for, but then deleted from, the upcoming (due out May 1, 2012) National Library of Australia publication Australian Backyard Naturalist, which is directed at readers aged about 10-14.  The majority of them might have trouble accessing or using a microscope, but if they can manage that, well, the information is here to allow them to go the extra mile, so to speak.  You don't need the book to use what you find there.

Click here if you are curious, otherwise, ignore this link.

That's the end of the commercial

The most unlikely puddles can turn out to be home to an amazing range of tiny plants and animals. I like to search puddles beside streams, but I also like searching the scrapings from reeds in a pool or a dam. Things like that often hold surprises. Every pond is a jungle, with animals eating plants and animals eating animals, though some of the smaller animals specialise in collecting scraps and bits. Nothing is wasted in an ecosystem—that's why it's called a system!

Basic microscopy equipment. From the top: backed razor
blade, eye-dropper, dissecting needle, forceps (tweezers),
Pasteur pipettes, brushes.

You will need a microscope, slides (and one well slide), cover slips, a dissecting needle to lay the cover slips down, a medium size camel hair brush, and an eye dropper or a Pasteur pipette (this is an eye dropper with a long drawn-out point). You may also need advice on how to use a microscope, but as soon as you feel ready, start looking at the water fleas or whatever else interests you. Remember Rule 1 of being a naturalist: the most interesting questions are your own questions!

You also need some live material.  Most ponds and still water will develop a collection of life over time, and if you take some green slime, you will normally take a good sample of this life, along with the "slime", otherwise called pond scum, which is actually an assortment of algae and quite a few motile forms that may or may not be animals in the strict sense. The methods for culture outlined in my last entry are probably more useful than going out to collect stuff from dubious drains.

The mistake most beginners make is putting too much material on a slide. Your microscope works when light shines through the stuff on the slide, and your cover slip has to lie down flat. If there is too much gunk, you can't see through it, and the cover slip does not sit down properly. When that happens, you end up with air bubbles which make it even harder to see details.

This is more the sort of thing you want to see. (I cheated here: this is another part of the same slide, but that doesn't matter, so long as there are less clumpy bits.  Practice makes perfect!

To master this trick, get a tiny amount of green slime from a pond, put it in a drop of water on a slide and add a cover slip. When you look at your first slide, it will always be too dark to see anything. Make a second slide, and this time, use even less slime, and spread it out with two needles or two pairs of forceps.

Even then, some parts of the slime will be too thick, so move the slide until you are looking through a less populated part, and focus on it under low power. Then, if something looks interesting, put it in the middle of the field of view, and move to a higher power. (This instruction will make more sense once you are used to working with a microscope.)

Take small amounts of "slime", and spread it out with a brush. If you have a fish tank, some of the most interesting gunk comes from the filter. Stir this up a bit, and then take some of the material with an eye dropper and put it in a Petri dish. With a black background and a strong light, you should be able to see if there are any tiny animals in the water. If there are, use a Pasteur pipette to take a sample. If there are no visible animals, use a flat slide, if you can see moving animals in the gunk with your naked eye, use a well slide.

When you switch to high power, you may see Paramecium (you can see one of these in the video which is in my last entry), some nematodes, or some of the other larger animals that live in green water. Paramecium is a single-celled animal with the common name "slipper animal", because they are shaped a bit like a slipper. They are ciliates, which means they move along by beating large numbers of short hairs called cilia.

The large ciliates feed on bacteria, yeasts and algae, all of which have smaller cells. Keep an eye out also for filamentous algae like Spirogyra. That one is easy to spot under the microscope because it has spiral chloroplasts.

(This one is not Spirogyra, but all filamentous algae are formed when a series of single cells link up to form a thread like this. This one is x400.)

Paramecium cells range in size from 50 µm to 350 µm, which means the largest ones will be just visible with a hand lens, if you are lucky. I see them most often as large dark blurs that shoot across my microscope's field of view, out of focus, when I am looking at something smaller, like diatoms.

Diatoms are single cells most of the time, but some of them form filaments, ribbons and even colonies. They have cell walls made of silica, and diatomaceous earth is formed from the remains of long-dead diatoms. There are probably 100,000 different diatom species around the world.

There are three diatoms in this picture, but two of them were on different levels and so more blurred. Viewed at x400.

To identify your algae, you will need a dichotomous key to the green algae, or the filamentous green algae. To search on the web, it will probably be better to enter a search string using the technical name for the green algae: <key freshwater chlorophyta> or <chlorophyta identification freshwater>. Leave out the "angle brackets".

Filamentous algae are called 'moss' and 'pond scum' when they attack fish ponds and tanks, where they often go out of control and end up dying to leave a decaying mass, riddled with bacteria which use up all the oxygen in the water, killing the fish. They are actually long strings of algal cells. Some of the most interesting filamentous algae can be found where water runs through channels in a rock. The cells in the filaments are too small to see with a hand lens, but you can see detail even under low power with a microscope.

Most of what you see will be algae. I suggest that you look up the following on the web and become familiar with the appearance of Spirogyra, Volvox, Scenedesmus, Nostoc and Chlamydomonas. As you track those down, you will probably see other familiar algae as well. One thing you are sure to find is rotifers.  I will finish this entry with a bit about them.

Rotifers

Oops! As oldsalt19 has pointed out, this is a protozoan
called Vorticella. Colour me absent-minded!

Rotifers are also called 'wheel animals', a name that refers to their cilia, which beat continuously as a way of catching food, and look like spinning wheels. You could call them worms if you wanted, but 'worm' can mean almost anything, because it isn't a scientific term.

Under the microscope, rotifers are always moving, trying to catch food. You can also see one in motion in the video in the previous blog entry.

Rotifers are quite small, about 100 to 500 microns (0.1 to 0.5 mm) long, though a few are as large as 2 mm. Mostly, they are found in fresh water, and the ones you will probably see are the sessile forms, the kind that grip onto something and stay there, but other rotifers are free-swimming, and some others 'inchworm' their way around.

From their size, you might think that they are single-celled protozoa, but they have multiple cells, an alimentary canal with a pharynx (think of it as a mouth) and an anus. They mainly eat single-celled algae like Chlorella, Euglena and Chlamydomonas.

Rotifers have a very simple nervous system. In many species, males are rare. No males are known at all for any member of the family which includes the genus Rotifer, and they reproduce by producing eggs which have a full set of chromosomes. (This is seriously specialised: look up <bdelloid rotifer diploid egg> for more information.)

To get some rotifers to study, collect some pond water and stand it on a window-sill in moderate light for a few days. The rotifers will collect near the top, where there is more oxygen, so you can pick them up with a pipette or an eye-dropper. You will also find some attached to filamentous algae and other bits and pieces in 'green slime'.

They also live in moss mats. If you soak a piece of moss mat in water and then squeeze it out over a bowl, you will generally find nematodes and rotifers. The method is supposed to produce tardigrades. I have never found tardigrades so far, but lots of rotifers!

I will come to the tardigrades next time.  They are cute, quite hard to catch, but here is the proof that I managed to catch one. This was so ferociously difficult that it had to go, because it would just put too many younger readers off. Still, for those with grit, determination, or just a plain stubborn streak, I will tell my tale and share what I learned.

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This blog covers quite a few different things, so I tag each post. I also blog about history, and I am currently writing a series of books called Not your usual... and the first two have been accepted by Five Mile Press, The offcuts appear here with the tag Not Your Usual... . For a taste of Australian tall tales, try the tags Speewah or Crooked Mick.   For a miscellany of oddities, try the tag temporary obsessions. And language us covered under the tags Descants and Curiosities, while stuff like this, all about small life is under Wee beasties.