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Salt Marshes

Salt marshes are coastal wetlands rich in marine life. They are sometimes called tidal marshes, because they occur in the zone between low and high tides. Salt marsh plants cannot grow where waves are strong, but they thrive along low-energy coasts. They also occur in areas called estuaries, where freshwater from the land mixes with sea water. A distinctive feature of salt marshes is the color - the plants are various shades of gray, brown and green.

What Are Salt Marshes?

Salt marshes are composed of a variety of plants: rushes, sedges and grasses. Florida's dominant salt marsh species include: black needle rush (Juncus roemerianus), the grayish rush occurring along higher marsh areas; saltmeadow cord grass (Spartina patens), growing in areas that are periodically inundated; smooth cord grass (Spartina alterniflora), found in the lowest areas that are most frequently inundated; and sawgrass (Cladium jamaicense), which is actually a freshwater plant that sometimes grows along the upper edges of salt marshes. All are tolerant of the salt in sea spray.

Salt marshes are important for many reasons. Hidden within the tangle of salt marsh plants are animals in various stages of life. Animals can hide from predators in marsh vegetation, because the shallow brackish area physically excludes larger fish. Many of Florida's popular marine fisheries species spend the early part of their lives protected in salt marshes.

Young fish often have a varied diet, foraging for food in the muds of the marsh bottom, on the plants themselves, and on smaller organisms that also dwell in the marsh system. As salt marsh plants die and decompose, they create organic detritus, another food source for many marsh dwellers. Tidal waters move up into the marsh and then retreat, distributing detritus throughout the estuary. Algae are also an important food source in salt marshes.

Florida's Salt Marshes

Salt marshes form along the margins of many north Florida estuaries. Gulf coast salt marshes occur along low energy shorelines, at the mouth of rivers, and in bays, bayous and sounds. The Panhandle region west of Apalachicola Bay consists mainly of estuaries with few salt marshes. However, from Apalachicola Bay south to Tampa Bay, salt marshes are the main form of coastal vegetation. The coastal area known as Big Bend has the greatest salt marsh acreage in Florida, extending from Apalachicola Bay to Cedar Key. South of Cedar Key salt marshes begin to be replaced by mangroves as the predominant intertidal plants. On the Atlantic Coast, salt marshes occur from Daytona Beach northward.

Despite their value, salt marshes are too often considered to be worthless. Salt marshes provide nursery areas for fishes, shellfish and crustaceans. These plants have extensive root systems that enable them to withstand brief storm surges, buffering the impact on upland areas. Salt marshes also act as filters. Tidal creeks meander through the marshes transporting valuable nutrients as well as pollutants from upland development. Salt marshes can absorb, or trap, some of these pollutants, reducing the pollutant load entering estuaries. Salt marshes also prevent sediments from washing offshore, often creating more land on which salt marshes can grow.

Salt Marsh Losses in Florida

Salt marsh systems are dynamic, constantly changing. Society, however, emphasizes stability and permanence. As a result, salt marshes have been drained or filled with silt, sand or refuse to an elevation at which they can no longer survive. It is estimated that in Florida at least 60,000 acres, or 8 percent, of estuarine habitat has been lost to permitted dredge and fill activities.

The Florida Marine Research Institute is studying changes in Florida's coastal habitats. Scientists can evaluate changes by comparing aerial photographs of the coast in the 1940s, 1950s and 1980s. Too frequently, the changes observed show loss of fisheries habitats.

Salt marsh loss has occurred in Florida's five northeast counties, which contain 11 percent of the state's total salt marsh acreage. The primary loss in Nassau County occurred because of dredging for the Intracoastal Waterway. Duval County has been impacted even more severely by human activity. Extending 3.5 miles on either side of St. Johns Inlet and 10 miles up the St. Johns River, analysis indicated a 36-percent loss of marsh habitat. The loss is primarily due to dredge and fill of marsh habitat since 1943.

In Palm Beach County, a 51-percent decrease in salt marsh acreage occurred in Lake Worth between 1944 and 1982 due to major land developments. A network of canals draining low lying uplands diverted the natural flow of freshwater away from salt marsh areas.

In southwest Florida, both salt marshes and mangroves occur along the Tampa Bay shore. Since 1940, Tampa Bay has been one of the fastest-growing metropolitan areas in Florida. Considerable environmental damage has occurred in Tampa Bay along with this growth. Four major types of dredging have impacted Tampa Bay during the last 100 years: channel deepening, maintenance dredging, shell dredging, and dredging for land fill construction. Ship channel dredging and port construction have brought Tampa Bay the economic benefits of being one of the largest ports in the nation. Tampa Bay has lost more than 40 percent of its original mangrove and salt marsh acreage over this time.

The elimination and alteration of Florida salt marshes have a negative effect on fishery resources. Estuaries provide nursery areas for at least 70 percent of Florida's important recreational and commercial fishes, shellfish and crustaceans. Many of Florida's marine fisheries will decline and may disappear without coastal wetlands.

State regulations have been enacted to protect Florida's salt marsh systems. Specifically, the Warren B. Henderson Wetlands Act of 1984 established clear guidelines for defining wetland areas that come under state jurisdiction. All dredging and filling activities in state waters require permits unless specifically exempted. Local laws vary, so be sure to check with officials in your area before taking any action.

Last Modified:
June 1, 2020 - 1:49pm

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