Abstract

Invasive species are an issue worldwide as humans and their global activities easily transport organisms long distances. One such species of seagrass, Halophila stipulacea, has spread from its native range in the Red Sea, to the Mediterranean Sea and subsequently to the Caribbean Sea where it has become widespread. This study evaluated the biodiversity associated with these new expansive seagrass beds to see if there may be some positive attributes associated with the invasion. In many areas, H. stipulacea is outcompeting native seagrasses likely leading to decreases in biodiversity and habitat complexity, but in other areas, it is populating once sandy substrate and possibly having the opposite effect. We surveyed two sites at both shallow and deeper depths off the leeward coast of St. Eustatius, using both belt transect and quadrat surveys. Divers identified and counted all fishes present within each belt transect and took pictures of 1m2 quadrats placed along each transect for analysis of the seagrasses and associated sessile species. The findings revealed a dominance of H. stipulacea (65.23% cover) and less than 2% cover of the native seagrasses: Syringodium filiforme and Halodule wrightii. More than 50 species of fishes were identified within or very close to the H. stipulacea beds. Approximately 25 species of algae, 21 molluscs, 18 crustaceans, 8 echinoderms, 4 polychaete worms, 14 sponges and 11 cnidarians were also encountered. The transition from sand to H. stipulacea appears to be increasing biodiversity and providing new ecological functions and services, highlighting the need for further study.

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