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The Microbes in Your Pond

By: Dr Gareth Evans - Updated: 9 Jul 2010 | comments*Discuss
Microbes Microscope Bacteria Protozoa

If you’ve ever looked down a microscope at a drop of pond water, you understand what people say about it teeming with life – and if you’ve ever wondered what all the talk of “biodiversity” is about, you needn’t look any further to find out. There’s a whole new world of predators and prey, tiny plants and miniature grazers to be found in every cubic millimetre, in shapes and forms as alien and bizarre as anything that you’ll ever see in a sci-fi movie.

Some of them have important jobs to do in helping maintain water quality, while others form the bottom of a food chain that ultimately helps support your fish – and all of them fit into the unique and isolated ecosystem that is your pond.


From what all of the disinfectant commercials say, you’d be forgiven for thinking that bacteria are something that you really don’t want to have lurking in your pond, but we’d all be in a right old state without them. Although many of them are responsible for diseases of one kind or another, by no means all of the world’s countless species of bacteria are – and many of these non-pathogenic examples perform beneficial functions. In this regard, probably two of the most important for aquatic enthusiasts – especially those with fish in their ponds – are Nitrosomonas and Nitrobacter which respectively turn ammonia into nitrite, and then nitrite into nitrate, forming important links in the nitrogen cycle.


Many of the micro-organism are single celled-animals belonging to the group known as the protozoa. They come in a variety of sizes and shapes, while some of them, such as arguably the most famous of the lot – amoeba – have no fixed shape at all, their jelly-like bodies having no “head-end” which allows them to flow in any direction. Ranking as some of the largest of their group, a big amoeba is just about visible to the naked eye – but don’t expect to be able to discern much detail! View one under even a modest microscope and you’ll be able to spot its nucleus – the ‘brain’ of the cell – the flowing body extensions called pseudopods (literally meaning “false-feet”) it uses to move around and with a bit of luck, the vacuoles which act like temporary stomach as it digests its meal.

Other kinds of protozoa swim actively, filtering out the bacteria they feed on from the water. Paramecium is a good example of this kind of organism, known in many of the older microscopy text-books as the “slipper animalcule” on the basis of its shape. Covered in short stiff hairs called cilia, which beat in order, this microbe propels itself around the pond, swimming forward and gently rotating along its own axis, funnelling bacteria and other small organic fragments into a long groove in its body which acts like a mouth. The whole creature is little more than the thickness of a human hair and yet such a remarkable amount of features are packed into its diminutive frame that it’s worth the price of a microscope to see this character alone!


Some of the tiny beasts you can find aren’t unicellular protozoa, even though they resemble them physically and are much the same size; they are rotifers and they’ve adopted the multi-cellular approach to life on a very, very small scale indeed. They’re named after the circular rings of cilia around their heads which help them swim and also waft bacteria into their mouths. Once they find a good feeding spot, they attach themselves to a suitable point with two toe-like structures at their tail ends, releasing and swimming away once they’ve had their fill. They are often to be found attached to small pieces of debris at the bottom of the pond, where there’s plenty to eat.


Algae are seldom welcome in an ornamental pond, but some of them are a lot less trouble – and a good deal more fascinating – than the kind that block up pumps and turn the water green! Euglena and Chlamydomonas, for example, are plants with a definite difference. Both are flagellates – possessing long whip-like structures called “flagella”, which they use to actively move around, as well as eye-spots that are light-sensitive. It’s hardly surprising that the debate has raged for years over whether organisms such as these should be viewed as plants, or animals!

Volvox is another common microscopic algae which is well worth a good look, if you happen to spot one in your pond water. This strange alga forms tiny football-shaped colonies made up of thousands of individual cells, all of which beat their cilia in unison to propel the spherical colony through the water. As the original group becomes mature, new colonies form within the hollow ball, and are eventually released once the old colony disintegrates. Seen through a microscope with the right lighting, it’s like watching Darth Vader’s Death Star in miniature gently spinning along.

For many people, it’s the lure of the wildlife to be found in and around the pond that drives them to build a water-feature in the first place. If the opportunity to get a slightly closer insight into the world of nature is a big part of your pond keeping pleasure, then it’s definitely worth thinking about investing a few pounds in a decent-quality microscope. There’s a whole zoo of microbes to be discovered in the smallest volumes of water and one thing’s for sure – the variety of life you’ll see doesn’t get much wilder than it does at this scale!

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