In the Everglades, periphyton, a dense mix of microscopic algae, fungi and bacteria, and floc, or large clumps of organic matter, form the base of the food web. Small fish, shrimp and other organisms eat this stuff. In turn, large fish and birds feed on small fish and shrimp, and alligators and other top predators feast on large fish and birds. Each of the players in this food web is both directly and indirectly affected by the amount of nutrients and water in the ecosystem. Such trophic dynamics are of particular interest to FCE-LTER scientists.
In Phase I of the project, scientists identified the food web players. To determine fish species composition and abundance, they used a 1-m2 throw trap at freshwater sites and a 9-m2 drop trap at mangrove sites to capture the animals. A mesh cage with openings on the top and bottom, a throw trap is tossed at random into the marsh and the animals that become trapped are scooped out, counted, and identified. A drop trap works the same way, except that it is dropped into place rather than tossed. This method is used when the throw trap is not feasible, such as in mangrove-dominated areas.
Once the players were identified, FCE-LTER researchers investigated the animals’ interactions with nutrients. They wanted to know how the availability of nutrients affects fish populations and how fish populations influence the availability of nutrients. To determine whether fish transport nutrients from the estuarine ecotone into the upstream marshes or into the downstream marine environments, scientists tagged individual fishes with transmitters and tracked them. Without killing them, samples were taken of the fishes’ tissues to quantify the nutrient content.