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Life in Freshwater

Adaptation to Stream Life

Sponges are permanently attached to the bottom of stones. This appears to be the best strategy when living in moving water otherwise the current will drag you off and away. However, there are real benefits in being flexible and able to move. A change in abiota, such as pollution, oxygen, pH and food, may require the organisms to find a better situation. If the stream dries out there would be few chances of survival. Very small organisms can live within what is known the boundary layer and prevent being displaced. This layer maybe around a millimetre and so the creature will have to be very small.

For the bulk of species, to minimise the chance of displacement, they need to be streamlined. For this the bulk of the body width needs to occupy less than 36% of the total body length. Ecdyonurus is a good example that has the bulk at the head end and is also flattened. This includes the legs and all this allows the animal to lie flat to the bottom substrate. Mayflies and stoneflies living in turbulent water have long tails that act as fins to assist the streamlining and recovery if they become dislodged. Suckers and suction-muscular feet, as in leeches and molluscs, hold the animal to the bottom. Riffle beetles have large claws on the feet for holding on. Pupal forms will be glued to the bottom, e.g. in caddis flies. Black flies have a suction pad that holds them down but if they are dislodged they have a safety line that they rapidly spin out and when it gets caught on the bottom they use the proleg to crawl back along it.


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