Invasive species are fauna and/or flora from another region of the world. Also known as Alien or exotic species, such species are introduced (mainly) to an area by ship ballast water, accidental release, and human activities. Invasive species can lead to the extinction of native plants and animals, impacting on biodiversity, and permanently alter habitats. Rugulopteryx okamurae, a brown alga, is one such invasive species that has taken hold within Gibraltar’s waters and has extensive distribution within Western Mediterranean, and as far west as Madeira and the Azores.