Undaria pinnatifida (Laminariales, Phaeophyta) 12 years after its introduction into the Atlantic Ocean

Abstract

Since its first introduction into the Atlantic for farming purposes in 1983, the brown alga Undaria pinnatifida has been found at several sites along the European coasts. The present study deals with an ecological experiment that was performed at the island of Ushant (Brittany, France) in order to check the ability of Undaria to recruit to a rocky substratum in situ. On the one hand, the authors were unsuccessful in getting Undaria to colonize a previously denuded area of shore, which was subsequently colonized by other native species, a result that may speak for a competition between Undaria and the local kelps. On the other hand, evidence is presented that Undaria pinnatifida has become a member of the Atlantic flora for good. The sporophytes can be found growing from low water mark of neap tide (+1.5 m) down to at least -15 m below lower water mark of spring tide. Its propagation is thought to occur in at least two ways: either step by step from cultivation sites along the coasts, or from the hulls of ships sailing from harbour to harbour. The preference of Undaria for settlement is on artificial structures.