The Salt Marsh

Spartina (formerly Spartina patens, now re-classified as Sporobolus alterniflorus), is a low marsh cordgrass, which has adapted to the harsh environments of high salt concentrations, consistently damp or water-covered soil and low oxygen levels. Frequently inundated by the tide, spartina is a highly specialized plant, adapted to grow in salt water. It is able to secrete salts that accumulate in it, through special glands in its leaves. Although its roots are embedded in thick mud which contains no oxygen, it is able to obtain oxygen through hollow tubes that reach all the way down from its leaves to its roots. It is native to the coasts of the Atlantic Ocean and forms dense colonies. Spartina (Sporobolus alterniflorus) has been planted by humans to reclaim estuarine areas for farming, to supply fodder for livestock, and to prevent erosion. These grasses provide rich habitat for crustaceans, mollusks, and birds, and serve as a major source of organic nutrients for the entire estuary. Mats of this salt hay grass are inhabited by many small animals and are an important food source for ducks and seaside sparrows. Spartina marshes serve as pollution filters and buffers against flooding and shoreline erosion.

Photo: ©Rory Mulligan
The tall reed phragmites (Phragmites Australis), grows in the foreground, closer to the land in mostly fresh water. The low growing spartina (Sporobolus alterniflorus) in the background grows in the salty seawater.

Spartina, a perennial deciduous grass, is cut by the force of incoming tides, wind, and rain. Its roots are continuously growing horizontal underground stems, which put out lateral shoots and roots at intervals, building up an ever more dense mat of organic material. Accumulating, year after year, layer upon layer, this fibrous organic matter, creates deep spongy beds filled with water. In the spartina beds live scud (Amphipoda), tiny crustaceans that live in the salt marsh and that number in the millions. They are detrivores, which contribute to decomposition and the nutrient cycles of the salt marsh. A salt marsh is one of the most productive ecosystems on earth. The tides constantly mix the waters. Harmful accumulations of waste products are diluted and removed. Nutrients are brought in constantly from sea and land. As a result, a salt marsh produces nearly ten tons of organic matter per acre every year. In comparison, the best hay only produces about four tons per acre. A salt marsh is an ever-growing organic buffer against storm surges and rising sea levels.

The very tough environment of the salt marsh, varying in the extremes, with high and low tides twice a day, limits the number of creatures and organisms that can adapt. Atlantic marsh fiddler crabs (Minuca pugnax) avoid being swept out to sea every high tide by digging holes to hide in and covering the openings with mud. They trap enough oxygen inside their holes to breathe underground, while the high tide engulfs the land above them. They emerge only as the tide goes out to sea, when they can safely forage in the sand. A variety of other crabs, snails, and worms find a home here. It is an important breeding ground for saltwater fish. With plenty to eat, fish lay their eggs here, and their fry are sheltered from the oceans, in the narrow channels between the mounds of spartina. During the warmer months, the mudflats provide an excellent foraging habitat for egrets and numerous species of herons, sandpipers, and plovers. Ducks and geese paddle through the channels year-round. Land animals, like raccoons (Procyon lotor), visit the salt marsh to feast on blue mussels, crab, shrimp, and fish.