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2000. The role of natural dispersal mechanisms in the spread of Undaria pinnalijida (Laminariales, Phaeophyceae). Phycologia 39: 547-553.The Asian kelp Undaria pinnalijida (Laminariales, Phaeophyceae) was first recorded in New Zealand in 1987 and has since' spread via shipping traffic and other vectors to a number of ports and harbours. Here we report the results of laboratory and field studies devised to assess the potential for natural dispersal of Undaria from a founding population. Under laboratory conditions, > 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 positioned 10 m down current of the release point. Field monitoring of a founding popUlation within the Marlborough Sounds, New Zealand, suggested that natural populations spread at least 100 m yr-l. 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 dispersal from fixed stands of Undaria results primarily in short-range spread (metres to hundreds of metres), with dispersal of fragments or whole sporophytes facilitating spread at scales of hundreds of metres to kilometres.