MEPS 339:123-130 (2007)  -  doi:10.3354/meps339123

Large-scale decline in offshore seagrass meadows in Bermuda

T. J. T. Murdoch1,*, A. F. Glasspool1, M. Outerbridge1, J. Ward2, S. Manuel2, J. Gray2, A. Nash2, K. A. Coates1,2, J. Pitt3, J. W. Fourqurean4, P. A. Barnes5, M. Vierros6, K. Holzer3,7, S. R. Smith3,8

1Bermuda Zoological Society, PO Box FL 145, Flatts, FL BX, Bermuda
2Bermuda Ministry of the Environment, Department of Conservation Services, PO Box FL 588, Flatts, FL BX, Bermuda
3Bermuda Institute of Ocean Sciences, 17 Biological Lane, St George’s, GE 01, Bermuda
4Florida International University, Department of Biological Sciences, 11200 SW 8th Street, Miami, Florida 33199, USA
5Malaspina University, 900 Fifth Street, Nanaimo, British Columbia N9R 5S5, Canada
6Secretariat of Convention on Biological Diversity, World Trade Center, 393 Saint Jacques Street, Suite 300, Montreal, Quebec H2Y 1N9, Canada
7University of Virginia, Department of Environmental Sciences, 219 McCormick Road, Charlottesville, Virgina 22904, USA
8Georgia State University, Department of Biology, PO Box 4010, Atlanta, Georgia 30303, USA

ABSTRACT: Bermuda is an isolated 5560 ha chain of limestone islands on a 150000 ha seamount located near 32°N, 64°W. Meadows of tropical and subtropical seagrasses, dominated by Thalassia testudinum and Syringodium filiforme, are found from inshore bays out to the inner edge of the rim reef that encircles the platform. Fine-scale computerized mapping and subsequent broad-scaled field assessment of seagrass meadows in Bermuda show that (1) meadows representing nearly one-quarter of the territory’s total seagrass area in 1997 had declined by 2004, (2) net loss of seagrass meadows occurred at rim reef and lagoonal locations that are far-removed from anthropogenic disturbances, (3) the decline appears to have been in progress as early as 1996, and (4) both T. testudinum and S. filiforme meadows declined. Nearly 2100 ha of meadows were visible in a 1997 geo-referenced mosaic of aerial photographs of the Bermuda platform. In 2004, 22 meadows that represented about 475 of the 900 ha of offshore seagrass identified in 1997 and earlier were absent or in obvious decline. The size and location of inshore and nearshore meadows, which are exposed to intense anthropogenic stresses and physical damage, varied over the same 7 yr but their total area has either remained unchanged or even increased. Processes contributing to the decline in offshore meadows have yet to be determined, but may include herbivory by juvenile green turtles and parrotfishes and below-normal productivity owing to a winter cold-water event correlated with a change in the North Atlantic Oscillation (NAO) in 1996. The potential consequences to Bermuda of the loss of nearly 500 ha of critical marine habitat are of extreme concern.


KEY WORDS: Benthic habitat mapping · Environmental monitoring · Thalassia testudinum · Syringodium filiforme · Seagrass die-off · Herbivory


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