Coastal wetlands are among the most productive ecosystems in the world, comparable to tropical rain forests and coral reefs. An immense variety of microbes, plants, insects, amphibians, reptiles, birds, fish, and mammals can be part of a natural wetland ecosystem. They provide great volumes of food that attract and support many animals. The combination of shallow water, high levels of nutrients, and high primary productivity is ideal for the development of organisms that form the base of the food web, supplying food for many species of fish, shellfish, insects, amphibians, birds, and mammals. The shallow water and sometimes dense plants are also ideal for sheltering animals from predators until the animals are big enough or fast enough to avoid predators outside the wetland.
Coastal wetlands are also important for keeping coastal waters clean.
They filter sediment and chemicals, reducing the amount of pollution that washes into bays and the ocean. The mixing of nutrients from land and sea that occurs in salt marshes produces more organic matter per acre than the richest Midwestern farmland. A small percentage of salt marsh grasses are eaten directly by fish and invertebrates, but most is decomposed by bacteria, producing an organic soup that feeds organisms such as amphipods, shrimp, crabs, snails, shellfish and finfish. These organisms in turn support a broad food chain that includes a variety of shellfish and finfish populations. Salt marshes are important to numerous species who are in the salt marsh only part-time.