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Gulf Coast Research Lab - Marine Botany |
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Chandeleur Islands Seagrass Monitoring |
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Dr. Patrick Biber Associate Professor, Coastal Sciences Gulf Coast Research Laboratory 703 East Beach Drive Ocean Springs, MS 39564 United States |
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Phone: 228 872 4200 Fax: 228 872 4204 E-mail: patrick.biber@usm.edu Webpage: |
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The Chandeleur Islands, LA are one of the more than 400 barrier islands in the United States. The island arc is located on the extreme eastern end of Louisiana, and approximately 25 miles due south of Biloxi, MS. As with many barrier islands along the Atlantic and Gulf coasts, seagrasses are found in the lee of the islands, protected from open oceanic conditions. Current projections for climate change include sea-level rise and increased (tropical) storm activity. Barrier islands are particularly vulnerable to these changes, and form a first line of defense. In the case of the Chandeleur Islands, recent hurricane activity has greatly reduced the area of emergent barriers, and therefore, the protection afforded to the extensive seagrass meadows. Since hurricane Georges in 1998, Katrina in 2005, and Gustav in 2008 seagrass area has declined dramatically, with some 500 acres lost in 2005 alone. These changes in island extent can be readily observed in Google Earth ver 5 or higher using the history timeline. |
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Images of the study area at 29o 58 N, 88o 50 W. The two transects with three sampling stations each are indicated. After hurricane Katrina (2005), the northern transect (stations L03 to L05) became substantially more exposed to wave and current energy than the southern transect (L12 to M02). Hurricanes Georges, Katrina, and Gustav passed over the study site in the past 10 years. Storm category (max. sustained wind speeds) for each storm is indicated, with a category 5 hurricane the most intense. Seagrass can be discerned on all images as a darker shading in the water immediately to the west (lee-side) of the emergent islands.
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Two studies have observed seagrasses in the former central, now northern, portions of this island chain. The 1998/1999 study was part of a larger seagrass assessment throughout the Gulf of Mexico, while the 2006-2010 study is a post-Katrina assessment. Six sites, in common to both studies, were visited. Sampling of seagrasses took place in April and September 2006, June 2008, and September 2011. Percent cover, species composition, plant morphometrics, tissue CNP, and sediment grain-size data were obtained. As in previous studies, seagrasses were not immediately impacted by hurricane winds and waves. However, the extreme loss of land resulted in much less protected conditions and erosion or burial of previous seagrass habitat was observed and documented. Similarly, the 2010 oil spill did not result in direct mortality of seagrasses, nonetheless, long term impacts of this additional stress on an already declining seagrass population is likely. |
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Images of the southern Chandeleur Islands being impacted by oil spilled from the BP Macondo well in May and June of 2010. The close proximity of these islands to the well-head means that this area experienced the most prolonged exposure to oil of all coastal areas. Clean up efforts were hampered by the remoteness of these islands, making access difficult for personnel and equipment used for clean up in other areas. The islands are an important bird rookery, especially for pelicans, and the impacts of the oil spill on these populations is still not completely known.
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