The increase in non-native marine species, introduced principally by aquaculture and in ballast water, is causing concern in Europe. One introduction of potential significance to kelp biotopes is the Japanese kelp, Undaria pinnatifida (wakame). This species has recently spread to the south coast of England from northern Brittany, where it was introduced for aquaculture, and it is thought likely to compete with the native Saccorhiza polyschides. The brief introduction of Macrocystis pyrifera to French waters in the 1970s, which was stopped by international pressure, could have had disastrous effects on all the native kelps and their associated biotopes. Macrocystis fronds can reach 60 m in length, and a single frond can gain 36 g per day, and thus would have competed with native species for space, light and nutrients.

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