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Botanica Marina

Editor-in-Chief: Dring, Matthew

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Assessment of propeller and off-road vehicle scarring in seagrass beds and wind-tidal flats of the southwestern Gulf of Mexico

Summer R. Martin1 / Christopher P. Onuf2 / Kenneth H. Dunton3

1The University of Texas at Austin Marine Science Institute, 750 Channel View Drive, Port Aransas, TX 78373, USA

2U.S. Geological Survey, National Wetlands Research Center, 6300 Ocean Drive, USGS-Unit 5838, Corpus Christi, TX 78412, USA

3The University of Texas at Austin Marine Science Institute, 750 Channel View Drive, Port Aransas, TX 78373, USA

Corresponding author

Citation Information: Botanica Marina. Volume 51, Issue 2, Pages 79–91, ISSN (Online) 14374323, ISSN (Print) 0006-8055, DOI: 10.1515/BOT.2008.015, May 2008

Publication History

Received:
2007-08-02
Accepted:
2008-01-14

Abstract

We used aerial photography and GIS to establish a quantitative baseline of propeller and off-road vehicle (ORV) scarring in seagrass and wind-tidal flats of the upper Laguna Madre in the Padre Island National Seashore (Texas, USA). We also examined scar recovery through comparison of recent (2002, 2005) and historical (1967) aerial photographs of the study area. Scarring intensity was calculated using two different methods. In the first, polygons were visually drawn around groups of scars on digital images. Scarring intensity was estimated as light (<5%), moderate (5–20%), or severe (>20%), based on the total coverage of scars within each polygon (taking into account the length, width, and density of scars). We developed a more objective method that employed creation of vector grid cells and buffers that incorporated the localized ecological impact of scars. Results of spatial and temporal analysis revealed that the polygon approach greatly underestimated the magnitude of scarring. For example, in a single photograph, 7% of seagrass area was lightly scarred according to the polygon method; but light scarring increased to 51% according to grid analysis of the same image. Our results also indicated that propeller scars in Halodule wrightii beds appear to recover in less than three years and ORV tracks have persisted in the wind-tidal flats for at least 38 years. Our approach provides resource managers with procedures for a more objective and efficient assessment of physical disturbances to seagrass and wind-tidal flats caused by boats and ORVs.

Keywords: Halodule wrightii; ORV tracks; propeller scarring; seagrass; wind-tidal flats

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