Most Unwanted: Wakame
Undaria pinnatifida
Habitat: Marine
Threat: Threatens native ecosystems and species
Status: Potential
This species has been nominated as among 100 of the "World's Worst" invaders
This is a species of seaweed that is native to the waters of Japan. Since the 1970’s the species has seen a dramatic increase in range due to human influence. Undaria pinnatifida first came to Europe in 1971 when it was introduced to France. The first record of Undaria pinnatifida in Britain was in 1994 when it was found attached to floating pontoons in the Hamble estuary in the Solent, Hampshire.
On a local scale, depending solely on natural means for dispersal, the species will spread roughly 10 km per year; however, rarely is this the case. The species ability to foul fishing equipment, spat, boats, mobile marine structures, and survive in ballast water, has accelerated the rate of spread to the order of 100’s of km a year.
What is it?
Undaria is a large brown species of kelp. The maximum length of Undaria fronds in the environment is 1.5m, but have been known to reach 3m. 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 m in clear waters, but the highest biomass is typically between 1 to 3 m in depth.
Impact
Undaria pinnatifida 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 it’s rapid growth rate, this species can colonise 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 Undaria 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.
Where is it from?
Originally native to Korea, Japan, and parts of China.
Where is it now?
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.
How can it get here?
Fouling of sea going vessels and marine aquaculture equipment.
Contamination of oyster spat and ballast water.
Potential for intentional introduction.
What you can do to prevent its arrival
Keep your boats and marine equipment free of fouling.
Report all sightings. .
