Scenedesmus
Scenedesmus is commonly found in the plankton of freshwater rivers, ponds, and lakes, and sometimes in brackish habitats. The genus has been found throughout all of North America from tropical to arctic climates. Growth may be dense in nutrient- rich waters but is not typically considered a nuisance. Like many other algae, Scenedesmus is an important primary producer and food source for higher trophic levels.
	The spines and bristles make the colonies more buoyant and allow them to uptake the light and nutrients that are more abundant near the surface, and may deter predation by herbivores. When threatened by a predator such as Daphnia, some species of Scenedesmus can form larger colonies with additional protective spines and tougher cell walls. The cell walls contain algaenans, which resist decay and thus contribute to the formation of fossil fuel deposits and visible fossil records.   Scenedesmus is a common bioindicator of physical and chemical changes in environmental conditions. The genus is commonly used to detect the presence of nutrients or toxins resulting from anthropogenic inputs to aquatic systems.