Life in Water
Rocky Fast Running Stream
Photographer - John Broomfield
Source - Museum Victoria
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Upland Stream with muddy substrate
Photographer - John Broomfield
Source - Museum Victoria
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Forest streams are usually well shaded. Thus little sunlight reaches the stream and the level of production of plant matter (known as primary production) is low. Consequently the potential for primary production in this habitat to support animal life is very limited. It has been discovered that forested streams rely on the input of organic matter from surrounding trees, usually as leaves but also as bark and wood, to fuel the food chain. This type of organic material is not readily digested by stream animals, but is soon colonised by a variety of aquatic fungi and bacteria that can decompose it. These microbes can in turn be digested by some aquatic insect larvae and other freshwater invertebrates that can chew up large pieces of organic matter such as leaves. The leaves are thus carriers of high quality food (the microbes) even though they themselves are not particularly valuable as a food source. As the leaves get chewed into smaller particles the surface area available for colonisation by fungi and bacteria increases and the decomposition process speeds up. Thus the decomposition of organic matter is a major pathway of energy flow in forested streams and is a important biological process that sustains the quality of these ecosystems.
Find out more about the animals that live in streams in the tall forests.
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