Periphyton refers to a complex, slimy layer of microscopic organisms and organic material that adheres to submerged surfaces in aquatic environments. This intricate community represents a significant component of freshwater and marine ecosystems. It forms a living carpet over underwater structures, playing a profound role in the health and function of these watery worlds.
What Periphyton Is
Periphyton is not a single organism but a diverse assemblage of microorganisms living together. It primarily consists of photosynthetic algae, such as diatoms, green algae, and cyanobacteria, which form the base of this community. Alongside these producers, various heterotrophic microbes like bacteria, fungi, and protozoa are also present, feeding on organic matter and other organisms within the community.
These diverse organisms are held together by an extracellular polymeric substance (EPS), a self-produced sticky matrix often described as a “slime.” This EPS is primarily composed of polysaccharides and proteins. The formation begins when pioneer organisms, often diatoms, attach to a submerged surface and excrete EPS, creating a foundational layer that then allows other organisms to colonize and grow within the developing matrix.
Where Periphyton Lives
Periphyton thrives in a wide range of aquatic habitats, from flowing streams and rivers to still lakes, ponds, and wetlands. This community attaches to nearly any submerged surface that receives sufficient light for photosynthesis. Common attachment points include natural substrates like rocks, pebbles, and submerged vegetation, as well as wood debris. Artificial structures like docks, piers, and even sediment particles can also host periphyton growth.
The growth and distribution of periphyton are influenced by environmental factors such as light penetration, nutrient availability, water temperature, and water flow. Shallow, clear waters with adequate sunlight and moderate flow often provide ideal conditions for periphyton development.
Periphyton’s Role in Ecosystems
Periphyton serves multiple functions within aquatic ecosystems, making it a fundamental component. One of its main roles is primary production, where the algal components convert sunlight into energy through photosynthesis, generating organic matter. This process forms the energetic foundation for many aquatic food webs, providing oxygen and organic compounds to the surrounding water.
The periphyton community acts as a direct food source for numerous aquatic organisms. Invertebrates, such as snails and insect larvae, graze on periphyton, as do certain fish species like mbuna cichlids in Lake Malawi, which have specialized teeth to scrape it from rocks. Tadpoles and other small consumers also rely on periphyton as a primary food source, linking this microbial layer to higher trophic levels.
Periphyton contributes significantly to nutrient cycling by absorbing and transforming dissolved nutrients from the water column. It takes up essential elements like nitrogen and phosphorus, which helps to remove excess nutrients and prevent their accumulation in the water. This nutrient uptake can also reduce turbidity in the water.
Beyond food and nutrient processing, periphyton also provides microhabitats and refuge for various small aquatic organisms. The complex, three-dimensional structure of the periphyton layer offers shelter and surfaces for attachment, contributing to the biodiversity of the aquatic environment. This creates a localized ecosystem within the larger body of water, supporting a variety of microbial and invertebrate life.
Periphyton and Environmental Health
Periphyton communities act as natural indicators of water quality, providing insights into the health of aquatic environments. Because periphyton is largely sessile, meaning it stays in one place, it cannot avoid contact with pollutants, making it highly responsive to changes in water chemistry. Alterations in its community structure, species composition, or abundance can signal environmental disturbances or pollution. For instance, certain diatom species are sensitive to acidic conditions, and their presence or absence can indicate changes in pH levels caused by pollution.
While periphyton is beneficial, excessive growth can indicate nutrient pollution, particularly from nitrogen and phosphorus. This overgrowth, often referred to as nuisance algal blooms, can lead to negative environmental impacts. When large amounts of periphyton die and decompose, they consume dissolved oxygen in the water, potentially leading to hypoxic or anoxic conditions that harm fish and other aquatic animals. Additionally, excessive periphyton can alter water pH, clog the spaces between gravel and sand, and make waterways less appealing for recreational activities. These blooms can also produce toxins, posing risks to aquatic life and human health.