Restoration of Damaged Seagrass Habitats
Seagrass habitat plays an important role in maintaining a diverse and healthy coastal ecosystem in Florida. Unfortunately, this valuable habitat is threatened by human activities. Coastal runoff from nearshore construction projects, dredge and fill operations, and micro-algal blooms can reduce the amount of light reaching the plants and may even smother them.
Operating a boat in water that is too shallow can result in propeller scars and blowholes. Propeller scars are created when the metal propeller, spinning at thousands of revolutions per minute, cuts deep into the root and rhizome system of the plants, leaving a furrow that can stretch across the grassbed. A depression called a blowhole forms when the boat operator grounds the boat and then tries to "motor off" using the engine. The engine not only digs in a circular shaped blowhole, but forces sediment into a pile or berm that covers and harms nearby grasses.
Blowholes and prop scars can take as long as seven to ten years to heal, primarily because seagrass plants are not capable of growing downward, away from light, into the damaged area. Currents can also wash away loose sediments and prevent the establishment of new plants. Repeated damage from boaters over time can result in habitat fragmentation and the erosion of the entire banktop.
A 1995 aerial survey of Florida's grassbeds conducted by State of Florida scientists found that boat propeller scars are found statewide, with moderate and severe scarring concentrated in areas with high populations of registered boaters such as the Florida Keys, Tampa Bay, Charlotte Harbor and the North Indian River Lagoon.
To address the loss of seagrass habitat due to boating impacts, scientists have developed techniques to repair damaged areas. The first step in the restoration process is to fill the scar or hole so that it is level with the surrounding area. Small rocks and gravel are used to fill the holes and scars first and a layer of finer sediments is placed on top. Shoal grass shoots are then carefully transplanted to the site. In time, this fast-growing species stabilizes loose sediments and promotes the establishment of the slower-growing climax species like turtle grass.
 In some sites, "bird stakes" are used in the restoration process. The relatively small T-shaped stakes, which are attractive bird perches, are pounded into the sediments along the length of the prop scar. Cormorants, terns, and other birds resting on the stakes defecate in the water, adding nutrients that promote the growth of seagrass, especially shoal grass. After one or two years, when the grass plants have established themselves, the stakes are removed to prevent over-fertilization of the site. Boaters and people traveling by car along the Overseas Highway in the Florida Keys have probably noticed rows of white stakes on restoration sites in nearshore waters. These, of course, are not to be confused with the taller red and green channel markers used for navigation. Although methods of restoration exist for damaged seagrass meadows, they are time and labor intensive. Prevention of groundings and prop dredging is the best way to protect this ecologically important habitat.
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