The hidden invasion of the alien seagrass Halophila stipulacea (Forsskal) Ascherson along Southeastern Italy

The seagrass Halophila stipulacea (Forsskal) Ascherson (Hydrocharitaceae) is a non-indigenous species (NIS) for the Medi-terranean Sea. This species is expected to have a high potential for invasiveness based on models predicting the present and future suitability of the Mediterranean coasts with respect to the plant requirements. This species was recorded for the first time along the Apulian coast in the Otranto harbor in 2011. Such a record was not considered in recent publications dealing with the species distribution and its forecasted invasion pathway, probably due to the scant information provided. One decade after its first record in the area, we confirmed the presence of the H. stipulacea meadow in the same locality (Otranto), and we identified four new H. stipulacea meadows along the Ionian coast are between 1 and 30 m deep in touristic areas. Indirect evidence suggests that the plant is actively spreading along the southeastern Italian coast, and monitoring programs aiming at mapping its distribution in the area, as well as its potential effect on the native biota, are required.