The dispersal of sporophytes ofUndaria pinnatifidaby coastal shipping in New Zealand, and implications for further dispersal ofUndariain France

Abstract

Sporophytes of the adventive Asian kelp Undaria pinnatifida, recently discovered growing in New Zealand and Tasmanian waters, are apparently spread by coastal shipping. Mature sporophytes, up to 1 m long and growing just below the waterline on the sides of ships, can be transported intact over hundreds of kilometres between New Zealand ports. The hulls of vessels can also be “seeded” with Undaria spores, and the gametophytes or the microscopic sporophytes transported to other harbours where the sporophytes mature. Commercial vessels, laid up pending sale and thus immobile for long periods, are especially prone to spread the plant because their waterline is at a constant depth. Such conditions permit the development of a fringing band of Undaria sporophytes along the ship's hull. In France Undaria was accidentally introduced to the Mediterranean coast near Sète before 1971, and intentionally planted on the coast of Brittany in 1983. The likely further dispersal of the kelp in this region is discussed in the light of these observations from New Zealand.