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Abstract Detail


Thorhaug, Anitra [1], Wanless, Harold [2], Schwarz, Arthur [3].

Seagrass Restoration after small vessel propeller scars: improved techniques.

Globally seagrass is decreases 7%y-1, putting 171,000 km2 global extent in peril. Technically feasible methodology for restoration (Van Katwijk, Thorhaug et al. 2016) are available but not political will to implement them among many nations. Ongoing damage to seagrass, decreases services seagrass provides: fisheries nurseries, nearshore resilience, and intense carbon sequestration, biodiversity. An improved method of repairing localized seagrass bed propeller scarring from small boaters is discussed. In Bear Cut, Biscayne Bay, Florida, on Florida’s far southeast coast, a new methodology was tested for healing the small vessel propeller scars found in 0-1m shallow waters throughout the Greater Caribbean Basin (including the Gulf of Mexico) and tropical/subtropical areas globally. We chose vessel scars of differing depths and breadth’s in a small harbor of mixed Thalassia and Halodule. First tested were a series of expandable, biodegradable non-toxic, materials to contain the sediment. The biodegradable tubes (7.5 cm wide and 45 cm) of expandable mesh-filled with local sediment matching the surrounding sediment were placed from 5 cm below the rim of scar, to the scar bottom, anchored with biodegradable anchors. Plugs of Halodule wrightii were planted at 0.5m intervals along the scar into the material. A series of control scars of were remained natural. The 3 month monitoring demonstrated sediment tubes in place, having settled into the scar depths and become a flattened top onto which further sediment had begun accumulating. Seagrass plugs laterally expanded down the scars. The 6mo. monitoring demonstrated buried tubes over which was an accumulated new sediment layer 0.5 to 2cm. Mesh fragments remained at depths from sediment tubes; top layers were degraded. Halodule plugs expanded substantially with a band of blades running lengthwise down the scars. The lateral apical meristem growth fitted the scar dimensions, stabilizing themselves via root growth into the sediment. The height of the scar was at 6 months level with surrounding height of surrounding sediment. At the 1 yr monitoring Halodule band down the scars had become complete, as the density increased from 1350bladesm-2 to 2950m-2. The surrounding Thalassia made incursions into the scar via expansion of rhizomes, dependent on depth. The method itself was first devised for decades of boat scarring in Florida Bay by Hall, et al (2012) and is applicable to small craft propeller. Larger scarring from large vessels and larger propellers have been solved by Thorhaug (2001) by a far different treatment.

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1 - Yale University, 1359 SW 22 Terrace, Miami, FL, 33145.0, United States
2 - University of Miami, Geology, 1320 S. Dixie Highway, Coral Gables, FL, 33146, USA
3 - Southwestern Adventist University, Biological Sciences, 100 W Hillcrest, Keene, TX, 76059, United States

Seagrasses sediment
Seagrass destruction
Sediment stabilization
Sediment baffle
Seagrass restoration
Sediment tubes.

Presentation Type: Oral Paper
Session: ECOPH1, Ecophysiology I
Location: San Pedro 2/Starr Pass
Date: Tuesday, July 30th, 2019
Time: 8:45 AM
Number: ECOPH1001
Abstract ID:268
Candidate for Awards:None

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