Seagrass Restoration Techniques

Once the injury assessment has been completed and damages are recovered from the responsible boater, the National Oceanic and Atmospheric Administration (NOAA) and the state of Florida scientists begin restoration work. The primary purposes of restoration are to prevent the injury from getting larger and to create the environmental conditions necessary for seagrass to recolonize the area. Depending on the size and severity of the injury, it often takes between 5 and 50 years for the injury to return to pregrounding conditions following restoration. Although there are many seagrass restoration techniques, the three most common are—

• Sediment fill
• Bird stakes
• Seagrass transplants

These restoration techniques are used at the grounding site and for compensatory restoration.

Sediment Fill

Sediment fill is used to return the injury site to pregrounding conditions. Photo courtesy of NOAA.

Newly created blowholes are very unstable. Because they usually have steep sides, blowholes are likely to expand as their walls crumble inward over time. In addition, blowholes can increase in size during strong storms such as hurricanes. To prevent injury expansion and to prepare the site for seagrass recolonization, scientists fill the blowhole with 0.25-inch crushed limestone rock. This material is very similar to the natural substrate found in the Florida Keys. Any injury with an escarpment, or dropoff, of more than 20 centimeters is a candidate to receive sediment fill because seagrass has a very difficult time growing in such excavations.

Bird Stakes

Bird roosting stakes speed seagrass recovery by taking advantage of a natural source of fertilizer. Photo courtesy of NOAA.

Like all plants, seagrasses need nutrients to grow. It is possible to encourage faster regrowth of seagrass in an injured area by fertilizing it with the needed nutrients. However, chemical fertilizer is expensive and needs to be replaced every few months. An alternative is to use a free, natural source of fertilizer—bird feces. Once an injury has been returned to grade with sediment fill, scientists install bird roosting stakes throughout the injury. These bird stakes extend 25 centimeters above the high water level and have a block on which birds can roost. After a hearty meal, birds come to rest on the stakes—and do what birds do after eating. The feces deposited by the roosting birds reach the bottom in concentrated doses, naturally fertilizing the area to encourage seagrass regrowth. Bird stakes are used when the injury occurs in less than 1.5 meters of water and are removed after approximately 18 months. The bird stakes are removed at this time because, if left in too long, they can lead to a community shift from turtle grass (Thalassia testudinum) to the fast-growing pioneer species. If the water is more than 1.5 meters deep, the feces do not reach the seafloor in concentrated doses. Commercial tree fertilizer spikes may be used for restoration in these deeper areas.

Seagrass Transplants

By planting fast-growing seagrass species, scientists immediately restore some of the environmental services that were lost due to the vessel grounding.

Once the site has been filled to grade and bird stakes have been installed, scientists collect seagrass from undamaged, adjacent areas and transplant them in the injury. Most seagrass beds in the Florida Keys are dominated by turtle grass, which is a slow-growing species that does not often survive if transplanted. Instead, scientists transplant faster-growing species (Halodule wrightii and Syringodium filiforme) that thrive in disturbed areas. By transplanting these seagrasses, scientists are immediately returning some of the ecological services that the area provided before the grounding. These fast-growing species also stabilize the sediment to allow the climax species, turtle grass, to return.