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Organisms found in aquatic ecosystems
Aquatic ecosystems usually contain a wide variety of life forms including bacteria, fungi, and protozoans; bottom-dwelling organisms such as insect larvae, snails, and worms; free-floating microscopic plants and animals known as plankton; large plants such as cattails, bulrushes, grasses, and reeds; and also fish, amphibians, reptiles, and birds. Viruses are also a significant part of the microbial ecology in natural waters and have recently been shown to play an important role in the nutrient and energy cycles.
The assemblages of these organisms vary from one ecosystem to another because the habitat conditions unique to each type of ecosystem tend to affect species distributions. For example, many rivers are relatively oxygen-rich and fast-flowing compared to lakes. The species adapted to these particular river conditions are rare or absent in the still waters of lakes and ponds.
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