Fate of two invasive or potentially invasive alien seaweeds in a central Mediterranean transitional water system: failure and success

Over the past 15 years, populations of two invasive or potentially invasive alien seaweeds have been studied by means of both quantitative and qualitative methods in the Mar Piccolo basin in Taranto (Southern Italy, Mediterranean Sea). The dynamics of the cold-temperate brown seaweed Undaria pinnatifida (Alariaceae, Laminariales) showed a boom-and-bust path, ending in apparent local extinction. In contrast, the tropical red seaweed Hypnea cornuta (Cystocloniaceae, Gigartinales) has shown a steadily invasive path since its introduction. The respective failure and success of these marine alien species were analysed in relation to their biological and ecological traits and the environmental characteristics of the Mar Piccolo in comparison with other Mediterranean coastal lagoons. The study confirms that temperature and salinity monitoring in the recipient region could provide a first estimation of the invasive potential of an alien species soon after its introduction.