Propeller scars in seagrass beds: An assessment and experimental study of recolonization in Weedon Island State Preserve, Florida

Durako, M; Hall, O; Sargent, F; Peck, S

Seagrass recolonization of experimentally scarred areas was monitored for 421 days within adjacent monospecific beds of turtle grass, Tbalassia testudinum Banks ex K6nig, and shoal grass, Halodule wriahtii Aschers., in Weedon Island State Preserve in Tampa Bay. Thalassia recovery data were fitted to a first order regression (y - 0.146x+8.18, r = 0.84) that indicated it would take approximately 3.6 - 6.4 years for these scars to achieve natural short-shoot densities (ca. 200-350 short-shoots 0.5 m~). Regrowth data for experimental scars in the Hal9dule bed fell into two distinct groups, depending on the location of the scars. The regression for data from the first group of subplots (y = 1.17x+17.0, r- 0.85), which were located near the fringe of the bed, indicated that natural short-shoot densities (ca. 1000-2000 short-shoots 0.5 m~) would be achieved after 2.3 - 4.6 years, whereas short-shoots in the second group of subplots (y = 3.03x-40.3, r = 0.84), which were located in the interior of the bed, would take only 0.9 - 1.8 years to reach natural densities. - Photogrammetric analyses of 1:2,400-, 1:12,000-, and 1:24,000-scale aerial photographs indicated that 1:24,000 scale photographs, taken under ideal conditions of water clarity, provided adequate resolution for identifying the areas damaged worst by propeller scars within the preserve. Seven hundred individual propeller scars were delineated using the 1:,2400-scale photography. The greatest concentration of propeller scars within the preserve occurred at the passes, and the maximum length of a single scar was approximately 800 m long.