Undaria pinnatifida

Do you think you have discovered an aquatic invasive species?

  1. Do not return the species to the water.
  2. Note the exact location (GPS coordinates) and the observation date.
  3. Take photos.
  4. Take note of identifying features.
  5. Report an Aquatic Invasive Species, depending on where you are.
  6. What you can do to reduce the risk.


Identifying features

Wakame is a large brown species of kelp. The maximum length of the fronds is 1.5 metres, but has been known to reach 3 metres. The seaweed has a branched holdfast (for attachment to the substrate) giving rise to a stipe (stem) just above the holdfast. The stipe has very wavy edges, giving it a ridged appearance. A broad, flattened leaf shaped blade is conspicuous. It has a distinct midrib and the margins of the blade are wavy. Found from low tide level down to 15 or 20 metres in clear waters, but the highest biomass is typically between 1 to 3 metres in depth.

Where it has been found

The species has been recorded in geographically distant places such as Argentina, Australia, Belgium, California, England France, New Zealand, Netherlands, Mexico, and Spain. The species is also recorded in Britain. This species has not yet been discovered in Canada’s freshwater ecosystems.

Potential ecological and economic impacts

Wakame is described as an opportunistic seaweed and has been observed to colonise new or disturbed substrata and artificial floating structures. It occurs in dense, vigorous stands, forming thick canopy over the biota in a wide range of shores and exposure. With its rapid growth rate, this species can colonize areas not typically inhabited by native seaweed species. This can drive ecosystem changes and Irish species may not be able to adapt to this change, however, the impacts of this species are, at present, poorly understood. It is possible that the presence of Wakame may alter the food resources of herbivores that would normally consume native species. Replacement of native seaweed species that have been grazed (or removed by seaweed harvesting) has also been suggested.


Native to Korea, Japan, and parts of China.

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