The occurrence of the tropical seagrass Halophila stipulacea (Hydrocharitaceae) is recorded for the first time on the Caribbean coast of Martinique (French West Indies, Caribbean Sea). Specimens were observed, since a large survey in 2006, on sandy substrates between 3 m and 32 m depths in this area. The species was found in mono-specific patches or mixed with other macrophytes as Syringodium filiforme (seagrass) and/or Ulva intestinalis (green alga). Halophila stipulacea was previously identified on the coasts of Dominica and St Lucia, two islands nearby our study area. While its presence was presumed to be in Martinique, it was never officially recorded. These findings off the coast of Martinique further define the distribution and widespread occurrence of this alien species within the Caribbean Sea.

The occurrence of the tropical seagrass species Halophila stipulacea (Hydrocharitaceae) is reported within the harbour of Palinuro (Salerno, central Tyrrhenian Sea, Italy). The bottom covered by the seagrass has been evaluated in about 16 m2, fragmented in various small patches distributed in a narrow belt between 0.5 and 5 m depth, and all settled on dead matte of the endemic Mediterranean seagrass Posidonia oceanica. Mean density was 10,500 shoots m−2. This record documents a displacement of about 180 km north of the previously documented limit of Halophila stipulacea in the western Mediterranean, likely mediated by pleasure boat traffic and anchoring, and favoured by climate change. This record illustrates a further example of the changing Mediterranean Sea biogeography: north–south patterns in biotic ranges will probably replace the presently well established west–east patterns in the Mediterranean Sea of tomorrow.