Wrangelia Penicillata (Rhodophyta, Ceramiales): Another Indigenous Invasive Species in the Mediterranean Sea?

The red alga Wrangelia penicillata is a photophilic species present within the infralittoral zone of several areas of the world. Although this species does not tend to form dense aggregations, we here report a case of massive proliferation observed at Tremiti Islands Marine Protected Area in June 2024. In fact, although it is not a non-indigenous species in the area, W. penicillata showed invasive traits within the archipelago. Two habitats of conservation importance were monitored: Posidonia oceanica meadows and coralligenous oucrops. Two sites per habitat were considered. Wrangelia penicillata was found widely covering these habitats between 15 and 25 m depth. Within all the four sites investigated, especially in the case of coralligenous habitat, this species was consistently the most frequent on the analyzed bottom areas, covering up to 100^% of the seabed.