Periphyton is an important indicator in the Greater Everglades. Periphyton is a key metric of the oligotrophic nutrient status. When marshes receive phosphorus at concentrations exceeding background levels, the microbes (algae, bacteria, fungi) comprising the periphyton mats of the Everglades remove the added phosphorus from the water. A series of ecological changes ensues, beginning with a change in species comprising the periphyton. Mat-forming blue-green algae and diatoms that are only found in the Everglades and other similar Caribbean wetlands (endemic species) are replaced by “weedy” species that occur in phosphorus-enriched environments all over the world. When the endemic species are replaced, the mats disintegrate, resulting in a loss of calcareous periphyton mat biomass that provides habitat and food for aquatic animals. Ultimately, a cascade of changes occurs that result in a transition to a cattail-dominated marsh. Because all of these ecosystem transitions resulting in a degraded state can occur without a change in water phosphorus concentration, periphyton serves as an important early-warning indicator of water quality degradation.

See the results for periphyton in the Greater Everglades.

Photo credit: Emily Nastase.

How is it measured?

Assessments for periphyton are based on a multi-metric approach using the concentration of total phosphorus in the periphyton, total biomass, and the percent of the diatom community comprised of endemic (versus cosmopolitan) species, developed from multi-scalar experiments and long-term observations. Using data from the Periphyton and Aquatic Fauna sampling for the Comprehensive Everglades Restoration Plan Monitoring and Assessment Program, each of 150 Principal Sampling Units across the Greater Everglades region were scored as impaired, cautionary, or baseline relative to regionally-expected values for total phosphorus, biomass, and endemic diatoms, and assigned a value of 0, 50, or 100%, respectively.