Abstract

The invasive marine Magnoliophyta Halophila stipulacea, originating from the Indian Ocean and the Red sea, was first observed in the Antilles, in 2002, in Grenada and reached Guadeloupe in 2011. Cartographies by video transect have shown that the species preferentially settled in sheltered areas on sandy to muddy sediments. H. stipulacea has largely colonized the bottoms of the bays of the leeward coast of Guadeloupe, from 3 to 55 m. Where present, this spe-cies has replaced indigenous species such as Syringodium filiforme and Halophila decipiens. The seagrass formed by H. Stipulacea presented linear growth rates varying from 0.9 ± 0.3 to 1.4 ± 0.1 cm per day according to the site. The maxi-mum recorded horizontal growth rate reached 7 cm per day. These values can explain the expansion success of this invader. According to the sites, total biomass (dry weight of leaves, rhizomes and roots) fluctuated from 172.6 ± 37.0 g/m2 to 308.8 ± 84.8 g/m2. Roots are short and the plant is weakly anchored in the sediment. This characteristic confers to this plant a low resistance to currents and surge. The leaf length varied between 3.8 ± 0.1 cm and 4.4 ± 0.1 cm. The small size of the leaves does not offers an important potential shelter to the associated macrofauna.A preliminary study of the macrofauna (> 2 mm) associated to this new species was performed with an epibenthic sledge completed by underwater visual surveys. A total of 148 invertebrates and 69 fish species were identi-fied.

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