Periphyton is a complex mixture ofalgae,cyanobacteria,heterotrophicmicrobes, anddetritus that is attached to submerged surfaces in most aquaticecosystems. The related termAufwuchs (German "surface growth" or "overgrowth",pronounced[ˈaʊ̯fˌvuːks]ⓘ) refers to the collection of small animals and plants that adhere to open surfaces in aquatic environments, such as parts of rooted plants.
Periphyton serves as an important food source forinvertebrates,tadpoles, and somefish. It can also absorbcontaminants, removing them from the water column and limiting their movement through the environment. The periphyton is also an important indicator ofwater quality; responses of this community topollutants can be measured at a variety of scales representingphysiological to community-level changes. Periphyton has often been used as an experimental system in, e.g.,pollution-induced community tolerance studies.
In both marine and freshwater environments,algae – particularlygreen algae anddiatoms – make up the dominant component of surface growth communities. Smallcrustaceans,rotifers, andprotozoans are also commonly found in fresh water and the sea, butinsect larvae,oligochaetes andtardigrades are peculiar to freshwater aufwuchs faunas.[citation needed]
Periphyton can contain species of cyanobacteria that are toxic to humans and other animals.[1] In fresh water, excessive growth and subsequent death and decay of periphyton can have undesirable effects: depleting oxygen in the water, altering itspH, and clogging the space between gravel and sand (thehyporheic zone). These effects, known aseutrophication, can impair or kill fishes and other animals, reduce the quality of drinking water, and make waterways unappealing for recreation. Remediating the damage to biodiversity and ecosystems caused by excessive periphyton growth costs billions of doillars annually.[2]
Conversely, periphyton can be damaged by urbanization: the increased turbidity levels associated withurban sprawl can smother periphyton, causing it to detach from the rocks on which it lives.
Periphyton communities are used inaquaculture food production systems for the removal of solid and dissolved pollutants. Their performance in filtration is established and their application as aquacultural feed is being researched. It can be important for the clearance of harmful chemicals and reducing turbidity.[citation needed]
Periphyton serves as an indicator of water quality[3] because:
Many aquatic animals feed extensively on periphyton. Thembunacichlids fromLake Malawi are particularly well known examples of fish adapted for feeding on periphyton. Examples includeLabeotropheus trewavasae andPseudotropheus zebra. They have scraper-like teeth that allow them to rasp the periphyton from rocks.[4] In marine communities, periphyton food sources are important for animals such aslimpets andsea urchins.[citation needed] Another amphibian that feasts on periphyton arespring peepers, small chorus frogs that occupy many ponds throughout Canada and the eastern United States.[5][6] Spring peepers filter periphyton from the environmental surfaces of their habitat.[5]