Undaria pinnatifida (Harvey) Suringar
Description: Thallus laminate, yellowish to
dark brown, usually 1-2 m, occasionally 3 m or more in length;
holdfast spreading, dichotomously branched and claw-like, giving
rise to a flattened oar-like stipe with a "fried-egg"
like margin with small proliferations and basally with
beautifully lobed sporophylls that coil around it when mature;
stipe continuing into the fond as a flattened midrib that bears
broadly lobed laciniate fronds with a roughly pyramidal
shape.
Habitat: Lower intertidal and very shallow
subtidal (no more than a few m), particularly in sheltered
locations, growing particularly on marinas, buoys, and similar
floating structures in harbours. Often occurring on
boat-hulls.
Distribution: In Ireland, Carrickfergus, Co.
Antrim (2014); Kilmore Quay, Co. Wexford (2016), Dun Laoghaire,
Co. Dublin (2017); Greystones, Co. Wicklow (2020). Now
widespread on the east coast in harbours and bays. Elsewhere in
Europe: S England, NW France, NW Spain, Mediterranean. Native to
Pacific Russia, Japan, China and Korea.
Key characteristics: Frilly sporophylls coiling
around the base of the flattened stipe at the base. A similar
flattened midrib is not found in any other kelp in the Atlantic.
Alaria esculenta has a midrib which is not flattened
and the frond of Alaria is not lobed, although it may
be similar laciniate.
Uses: Cultivated and collected in the wild in
Japan, China and Korea for
human consumption
as "Wakame" (Japan) and cultivation on ropes was
successfully carried out in Brittany for a time. Fucuiodan from
Wakame may be effective in the
prevention of certain cancers.
Notes: This is an introduced kelp from the W
Pacific, now found in the NE Atlantic and the W Mediterranean.
Elsewhere similar adventive populations have been found in New
Zealand, Tasmania, and Argentina. It is thought to have been
introduced into the southern hemisphere by fishing fleets from
SE Asia. The plants shown here are from Tasmania.
Undaria is a particular pest in Venice (see bottom two
pictures) where plants foul the step leading to St Mark's Square
(right) and cover the anchor chains of the
vaporetto and traghetto stops (left).
Common names: Wakame, Japanese Kelp.
References
Kraan, S. (2017). Undaria marching on; late arrival in the Republic of Ireland. Journal of Applied Phycology 29(2): 1107-1114.
Minchin, D. & Nunn, J. (2014). The invasive brown alga Undaria pinnatifida (Harvey) Suringar, 1873 (Laminariales: Alariaceae), spreads northwards in Europe. BioInvasions Records 3(2): 57-63.
Identification guide for selected marine non-native species (National Museum Wales). (Download free PDF, about 3.5 Mb).
Photographs © Dan Minchin (top and middle from N. Ireland);
M.D. Guiry
(bottom two from Venice).
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