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The Expansion of Halophila stipulacea (Hydrocharitaceae, Angiospermae) is Changing the Seagrass Landscape in the Commonwealth of Dominica, Lesser Antilles
Sascha C.C. Steiner1,* and Demian A. Willette2
1Institute for Tropical Marine Ecology, PO Box 36, Roseau, Commonwealth of Dominica. 2Department of Ecology and Evolutionary Biology, University of California - Los Angeles, Los Angeles CA 90095, USA. *Corresponding author.
Caribbean Naturalist, No. 25 (2015)
Abstract
The seagrass Halophila stipulacea, alien to the Caribbean, was first reported from Dominica in 2007, where its rapid growth and ability to supplant native species, as well as the profiles of native seagrasses meadows, were established in 2008. In 2013, we reexamined 27 meadows and observed a highly altered underwater landscape along Dominica’s west coast (leeward) and unchanged seagrass beds along the northeast (windward). On the western sublittoral, pure stands of H. stipulacea replaced most Syringodium filiforme meadows and Halodule wrightii in depths greater than 4 m, as well as all Halophila decipiens stands and meadows. Fauna and flora occurring within seagrasses was concentrated in the remaining native seagrass stands. We identified three scenarios of increasing impact by H. stipulacea: “native strongholds” of pure native stands, “invasive takeovers” where native seagrasses were completely replaced, and “new meadows” in areas previously free of seagrasses. The area covered by Dominica’s seagrasses doubled from an estimated 316 ha in 2008 to 773 ha in 2013; driven exclusively by the spread of the alien seagrass. Benefits and losses of the recent angiosperm invasion are unforeseeable, yet the remaining strongholds and the unchanged north coast meadows point at ecological limitations in the invasibility of native seagrasses and environmental circumstances that foster refugia for some native species. However, based on the increasing number of sightings H. stipulacea in the Lesser Antilles, we predict large-scale alterations in the architecture and species composition of seagrass meadows throughout the Caribbean within the next decade, and the demise of H. decipiens.
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