MPA Tip: On restoring seagrass after vessel damage

MPA News

"MPA Tip" is a recurring feature that presents advice on MPA planning and management gathered from practitioners and publications. Below we describe an innovative technique for restoring damaged seagrass beds. If you have a useful tip for addressing a problem in MPA planning or management, please tell us about it at mpanews [at] u.washington.edu. We would like to feature it in a future issue of MPA News.

Seagrasses are underwater plants that provide vital services to marine ecosystems, both as food and habitat. They often occur in extensive "meadows" in nearshore waters, and their shallow location exposes them to multiple stressors, including damage from vessel propellers and anchors. The Florida Keys National Marine Sanctuary in the U.S. has experimented with a technique to restore seagrass habitats scarred by vessels. In short, it involves planting posts ("bird stakes") in the damaged areas to encourage seabirds to land there. Over time, the birds' excrement serves as an effective fertilizer for re-establishing seagrass in the scarred areas. The research publications listed at bottom detail the success of the technique.

"Damage by vessels, particularly propeller scars, lends itself to rehabilitation by bird stakes," says Brian Keller, southeast regional science coordinator for the U.S. Office of National Marine Sanctuaries. "This is because the width of the damage can be in-filled by seagrasses, particularly 'weedy' species such as Halodule wrightii in the Florida Keys system, without sediment stabilization or addition. Small or narrow areas of damage lend themselves best to this approach."

Keller notes that bird stakes will not be effective in all seagrass-rehabilitation cases. Larger areas of vessel damage benefit more from other measures, including sediment fill and sediment tubes as described in the publications below. And bird stakes could actually be counterproductive in cases where seagrass habitat has been degraded by nutrient loading from land-based pollution sources, a major cause of seagrass decline worldwide. "Factors such as nutrient loading are best addressed at the source," says Keller.

For detailed descriptions of the bird stake approach and other methods of restoring vessel-damaged seagrass:

Final Programmatic Environmental Impact Statement for Seagrass Restoration In the Florida Keys National Marine Sanctuary
http://sanctuaries.noaa.gov/library/fk/seagrass_fpeis04.pdf

2002 - 03 Florida Keys National Marine Sanctuary Science Report: An Ecosystem Report Card After Five Years of Marine Zoning
http://sanctuaries.noaa.gov/science/conservation/fk_report.html

Case Studies: Paying for Seagrass Restoration in the Florida Keys
www.csc.noaa.gov/mpass/casestudies_floridakeys.html