The role of natural dispersal mechanisms in the spread of Undaria pinnatifida (Laminariales, Phaeophyceae)

The Asian kelp Undaria pinnatifida (Laminariales, Phaeophyceae) was first r ecorded in New Zealand in 1987 and has since spread via shipping traffic an d other vectors to a number of ports and harbours. Here we report the resul ts of laboratory and field studies devised to assess the potential for natu ral dispersal of Undaria from a founding population. Under laboratory condi tions, > 90% of Undaria spores were viable in seawater for at least 5 days, with some viable after 14 days. Spores artificially released into a tidal current resulted later in sporophytes appearing on artificial surfaces posi tioned 10 m down-current of the release point. Field monitoring of a foundi ng population within the Marlborough Sounds, New Zealand, suggested that na tural populations spread at least 100 m yr(-1). Reasons for the differences between the dispersal distances of the artificially released spores (10 m) and natural populations (100 m) are discussed. We propose that spore dispe rsal from fixed stands of (Indaria results primarily in short-range spread (metres to hundreds of metres), with dispersal of fragments or whole sporop hytes facilitating spread at scales of hundreds of metres to kilometres.