Researchers are working to develop a cost-effective, reliable procedure to accelerate recovery of seagrass habitats.
A 2012 report by Fish and Wildlife Research Institute (FWRI) Habitat Research biologists revealed insights from an ongoing study to accelerate the recovery of Florida Keys turtle grass (Thalassia testudinum) meadows severely damaged by vessel groundings.
Turtle grass, a type of seagrass, is a flowering plant that lives completely submerged in marine and estuarine waters, and a valuable part of Florida's marine environment. It helps maintain water clarity, stabilizes the bottom and provides food and shelter for fish and wildlife. Many turtle grass beds, however, have crisscrossing scars from vessels that have run aground and left holes empty of seagrass.
It can take years, or even decades, for slow-growing turtle grass to cover the scars naturally, and without the dense mat created by seagrass roots, high wind and waves carry away the fine sediment of the ocean floor, eroding and deepening the scars. To reverse this damage, FWRI biologists in 2008 initiated a study to develop a cost-effective, reliable procedure to accelerate recovery of turtle grass habitats by planting two fast-growing species – Halodule wrightii and Syringodium filiforme. They tested two planting treatments for helping meadows recover in Florida Keys waters, where seagrass scarring is widespread.
Scientists filled all the scars with pea rock (crushed limestone) to stabilize the area and prevent further erosion. Next, small bunches of fast-growing seagrasses were planted into one of two treatments. The first involved planting the seagrass directly into the pea rock. In the second, seagrass bunches were planted into biodegradable fabric tubes (Sediment Tubes) filled with screened carbonate sand and placed on top of the pea rock. The sand in the tubes is similar to the fine sediment in which seagrass normally grows. Over time, the tube's fabric covering decomposed and left the area covered with the carbonate sand, allowing seagrasses to take root and stabilize the sediment. Researchers installed into each treatment PVC stakes topped with wooden blocks so seabirds would roost and defecate, providing natural fertilizer to the fast-growing seagrass. Scientists tested these methods in low-energy, or calm, environments and high-energy areas with swift currents, powerful tides and lots of wave action.
The study has shown filling an injury with pea rock was effective at stabilizing scars and inhibiting further scouring in high- and low-energy locations. Sediment Tubes planted with fast-growing seagrass and fertilized with bird stakes promoted rapid seagrass colonization of scars in low-energy areas; however, they were not effective at the high-energy location. Fast-growing seagrass from the adjacent meadow was the primary source of seagrass colonizing the tube and the bare pea rock treatments at the high-energy site. This was also true for the pea rock treatment at the low-energy site. Seagrass planted directly into bare pea rock did not appear to survive for more than few months, indicating this may not be an effective restoration tool unless used in combination with Sediment Tubes.
Overall, the methods developed did successfully promote cover of fast-growing seagrasses – the critical first step in long-term recolonization of turtle grass. With the blowholes now filled and the sediment stabilized, researchers are observing small amounts of turtle grass growing back into the edges of the sites. The next step is to monitor the recovery of this slow-growing species.