Abstract

The Seagrass species Halophila stipulacea has invaded the French Antilles Islands since 2006. In Guadeloupe Island, H. stipulacea has mainly colonized the sheltered leeward coasts and embayments between the surface to 60 m deep. Native Syringodium filiforme and Halophila decipiens were widely eradicated from the coasts of the Island. Thalassia testudinum seagrass beds better resisted, due to the highly developed structures of their rhizosphere. Nowadays, Halophila seagrass beds constitute the most important surface of seagrass beds on the coasts of Guadeloupe Island. Benthic and fish communities associated with Halophila were studied and their biodiversity compared to those of the main native seagrass beds (Thalassia and Syringodium). Concerning benthic communities, 161 macroorganisms (48 algae and 113 animals) were identified in the three types of seagrass beds: 135 in Thalassia, 72 in Halophila and 48 Syringodium seagrass beds. The community of Halophila seagrass beds appeared to be an impoverished subset of that of Thalassia. A total of 181 fish species were recorded: 153 associated with Thalassia, 88 with Halophila and 19 with Syringodium seagrass beds. Most of them were juveniles. Fish abundances were similar in Thalassia and Halophila seagrass beds and the role of nursery of the seagrass beds created by the invasive species was equivalent to that of Thalassia. Thus, in spite of its detrimental effect on native seagrass, Halophila stipulacea increases the bottom surface colonized by seagrass beds and provides ecosystems services in terms of biodiversity and nursery for benthic organisms and fish, some of them of commercial interest.

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