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Seagrass Conservation Issues Quick Topics

Seagrass habitat has declined from approximately 5 million to 2.2 million acres since the 1950s and continues to face several threats, including coastal engineering projects, water clarity and quality issues, and boating impacts.

Coastal engineering projects such as beach renourishment, dredge and fill operations, and urban development like bridges or docks, can dig up existing seagrass beds, bury them with excess fill or both. Shoreline armoring can damage seagrasses by redirecting or intensifying currents and tidal action which can either result in erosion or sediments being dumped on the seagrass beds. Construction activities can also damage nearby seagrass beds by stirring up sediment and creating water clarity issues.

Prop scar

Prop scars are often visible from the air.

Water quality and water clarity is another issue that has been contributing to seagrass losses. Seagrasses are very dependent on sunlight. High turbidity can impede growth or even kill seagrasses. Turbidity can come from sediments that are suspended in the water or from excessive phytoplankton growth. Each can be impacted by humans. Both land-based and off-shore construction can result in sediments being carried away from the site and into the water. Phytoplankton and algal growth can be stimulated by excessive nutrients, such as fertilizer running off the land.

The third major issue facing seagrass communities are from boating. Boats can affect turbidity by kicking up sediment in high traffic areas, but the main impact from boating is from direct damage such as propeller scars, or prop scars. Prop scarring occurs in shallow water when a boat’s propeller tears and cuts up seagrass roots, stems and leaves, leaving a long, narrow furrow devoid of seagrasses. This damage can take 8 to 10 years to repair and with severe scarring these areas may never completely recover. Although linear features are most often associated with prop scars, some areas of seagrass habitats have been completely denuded by repeated scarring. In other instances, a linear scar can become a larger feature if the sediments are scoured to undercut the seagrass bed. This erosion can result in detachment of large sections of seagrasses that then float away leaving behind patches of bare sediment wider than the original prop scar.

 

Last updated: March 04, 2013

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