River biota

Abstract The river biota ranges widely in size (over 16 orders of magnitude), though most of its constituents are small and inconspicuous. Their biodiversity is impressive relative to the surface area of the globe covered by running waters. Microorganisms are numerous and dominate ecosystem processes like decomposition. They consist of viruses, bacteria, Archaea, fungi and smaller algae. There are then larger algae, lower and vascular plants. These are joined by protozoans and small metazoans (multicellular animals). Larger invertebrates include flatworms, molluscs, crustaceans and leeches. The most abundant animals are often insects, some aquatic only as larvae, some as both larva and adult. Fish are the most conspicuous and diverse vertebrates. Amphibians are numerous but highly threatened. Many birds depend on freshwater habitats, about 70 species being running-water specialists. There are many semi-aquatic mammals, two orders of fully aquatic mammals (river dolphins, and dugongs and manatees), while many others depend directly on rivers.