Distribution of the seagrass Halophila stipulacea: A big jump to the northwestern Mediterranean Sea

The Red Sea and Indian Ocean seagrass Halophila stipulacea entered the Mediterranean in the late 19th century via the Suez Canal. Here, we report on the discovery of a population of H. stipulacea covering 16.5 ha off the harbour of Cannes, French Riviera, France. This represents the northernmost locality of the species and a jump of 350 km to the north from its closest western Mediterranean locality (Razza di Juncu in Sardinia). At Cannes, it was found dwelling between 11 and 17 m depth on a dead matte of Posidonia oceanica. The species has most probably been introduced through mega-yacht or cruise ship anchoring since the Bay of Cannes is among the most highly-frequented places for luxury yachting and tourism. The lack of effective regulation to prevent the introduction of non-indigenous species in France and Europe is highlighted.