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Foundations of an Ecosystem
While Big Cypress National Preserve is best known for its cypress swamps, over 23 percent of the Preserve is a freshwater marl prairie ecosystem. These prairies are home to many organisms, and yet one of its most abundant and important lifeforms is more commonly stepped on and ignored than noticed. Have you ever walked into a prairie and observed a grayish-green or yellow-brown material coating the surface of soil, limestone, and plants in every direction? Derived from the Greek word elements "peri-", meaning around, and "phyton," meaning plant, periphyton does appear to be growing all over marl prairies. Few people realize that when you pick up a piece of this spongy, soggy mat, you hold much more than a plant. Periphyton is an entire community of organisms, including blue-green algae, fungi, microbes, bacteria, plant detritus, and animals that together compose the foundation of an entire ecosystem.
One example of periphyton's importance to freshwater marl prairies is its role as a primary producer.Primary producers collect energy from the sun and convert it, through a process called photosynthesis, into energy that allows them to grow. The blue-green algae found in periphyton are primary producers, and they give periphyton its green colors. When primary producers are eaten, they pass on the energy they collected from the sun to other organisms, known as consumers, that can't make energy from the sun. Examples of animals that are consumers of periphyton include snails, frogs, aquatic insects, and fish. These small creatures can be consumed by larger animals, such as wading birds. In this way, energy from the sun originally collected at the base of the food web by periphyton can be transferred to the top predators in the marl prairie. Without periphyton, the food web of the freshwater marl prairie would collapse.
In addition to capturing the sun's energy, periphyton conducting photosynthesis also create an additional byproduct: oxygen. On bright sunny afternoons, so much oxygen gas can be produced that periphyton can float up to the water's surface, buoyed up as though floating on inflatable rafts. Oxygen made by periphyton can dissolve into the water column and is essential for the survival of animals with gills, such as small fish, tadpoles, and aquatic insects. Without dissolved oxygen produced by periphyton, these creatures would suffocate.
Periphyton creates another crucial byproduct during photosynthesis, but this time the byproduct is essential for plants: soil. While plants in these freshwater marl prairies can't grow roots into rocks, they can grow roots into soil. But where does the soil come from? If you answered "periphyton," you are right! When periphyton conducts photosynthesis, it consumes acids in the water column. Since there is less acid, the pH of the water increases. This increase in pH causes dissolved calcium in the water to solidify on the surface of periphyton, other plants, or rocks. It is calcium that gives periphyton its gray or yellow-brown color. During the dry season, the organic material in the periphyton is eaten, but the calcium remains behind. Over time, this calcium builds up on the ground and creates a soil that is called marl (also called calcitic mud). Therefore, the plants of freshwater marl prairies, including sawgrass, muhly grass, and dwarf cypress, are also dependent on periphyton to survive.
Not only does Periphyton create a home for plants in freshwater marl prairies, it also provides a habitat for numerous small, burrowing creatures. Pick up a piece of periphyton and carefully observe it. You may find small worms, insects, or eggs hiding on its surface or inside the periphyton. Because periphyton absorbs water, these animals will also be able to find sources of moisture here even after the water in the prairie has dried up.
Finally, periphyton provides scientists with a natural and historical indicator of ecosystem health. Periphyton is easily affected by changes in the environment, especially nutrient levels and water levels. If nutrient levels, such as phosphorus, become too high, periphyton can be damaged and be outcompeted by other plants that thrive in areas with elevated phosphorus, such as cattails. If scientists begin to observe a shift from periphyton to cattail vegetation, it is an early warning sign that the freshwater marl prairie ecosystem is unhealthy. Additionally, scientists who find marl buried in soils can analyze it to understand water and nutrient conditions hundreds or thousands of years ago.
While periphyton may not appear significant at first glance, it is amazing to consider how many ways this small community of organisms can influence their surrounding environment. The founders of a food web, regulators of water quality, creators of soil, builders of homes, reservoirs of water, and indicators of current and historical ecosystem health: you may begin to wonder what periphyton cannot do! The next time you decide to take a walk through a wet marl prairie, make sure to look down and observe the periphyton all around you and consider what your surrounding landscape would look like without this small, yet essential community.
Last updated: May 4, 2020