MICROCOSMOS.NL - Where do the animals live in the ditch?

INTRODUCTION   THE SURFACE   THE WATERPLANTS   THE SOIL

Where are the creatures in the ditch? The first thought is that they are all just swimming around there all the time, but in reality there are but few species that do so. Fish, of course. A fish floats in the water thanks to a swim bladder, which makes the weight of the displaced water exactly equal to its own body weight. And so you can see a roach or stickleback hanging around quietly, in all kinds of positions. But despite those fish, your coarse-mesh landing net usually remains empty when you drag it through the free water. There is an understandable reason for this: all sentient animals dart away, when that terrifying thing plunges into the ditch, which to the animals may seem like the beak of a hungry heron. And even when you were walking towards the water, many ditch dwellers fled to their hiding places, scared by your looming silhouette and the vibrations of your footsteps. That is why it is good to first wait quietly and calmly, for fifteen minutes or so, near a beautiful ditch. Then finally the larger animals will emerge. Only the apparently unsuspecting tadpoles are easy to see and catch in the spring, when they are actively swimming around.

If you drag a fine mesh net through the open water, you may find a multitude of animals in it, especially in the warmer months. For example, ghostlarvae of the phantom midge, which float in the water thanks to their four tiny swim bladders. And of course waterfleas (mostly daphnias), in flocks that seem like red clouds in the summerwater. They keep floating by constantly making downward strokes with their antennae, when that movement stops, a water flea sinks to the bottom. Copepods, which resemble water fleas (e.g. eudiaptomus), can also occur en masse. Then there is the fish louse that, in search of a fish, swims through the water like a miniature flatfish. And swimming water mites. But that's about it as far as open water goes, aside from accidental bycatch.

The community in the ditch forms a food chain, of which every organism is a part. And so there is a major disadvantage to open water: you are more conspicious there, which is disadvantageous for both prey and hunter. That is why fish are often dark colored on the back and smaller animals are very transparent. Sunlight may be beneficial, but food and security are scarce in open space. You will also see that a lot of time is spent in places with more hiding options. Many insect species live underwater in much the same way as their counterparts on dry land, with only some adaptations for breathing. Those who can swim often only do so, to get from one habitat to another in a short time.

We can identify three important habitats in the ditch: the water surface, the aquatic plants and the soil. Even an excellent swimmer like the Great Divingbeetle only swims through the open water for a small part of the day, from one resting place to another: it 'hangs' breathing on the surface, sits among the water plants, or under a stone at the bottom and takes refuge as best as possible. More about the three habitats on the following pages.

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