Undaria pinnatifida | Wakame

Pre 2017

2017 - 2020


Conservation status

Not Assessed

Legal status

Third Schedule listed species under Regulations 49 & 50 in the European Communities (Birds and Natural Habitats) Regulations 2011. (Note: Regulation 50 not yet enacted).

Listed as a schedule 9 species under Articles 15 & 15A of the Wildlife Order (Northern Ireland) 1985 (Article 15A not yet enacted).

Native status


First reported in the wild



Invasive species - risk of High Impact

Irish status


Introduction pathways - 1

Transport Stowaway

Introduction pathways subclass - 1

Ship/boat hull fouling

Invasive score


NAPRA Ireland risk assessed


Species Biology


Annual brown algae with a lifecycle consisting of a macroscopic stage (the sporophyte), and a microscopic stage (the gametophyte) (Verlaque, 2007).

The sporophyte is the stage that can be readily identified is a large golden brown seaweed 1-3m in length, with a broad, 'strap like' midrib (1-3cm wide) running the length of the thallus (Verlaque, 2007).

Possible identity confusion with Alaria esculenta & Laminaria spp.


On man-made structures in Torquay Marina U. pinnatifida was found to decrease the numbers of Laminaria digitata, L. saccharina (two native sea weeds) and the tunicate Styela clava (an invasive tunicate) (Farrell & Fletcher, 2006), and has been shown to impact on native seaweeds in Argentina (Casas et al., 2004). These impacts are likely to be more severe in natural habitats (Casas et al., 2004; Farrell & Fletcher, 2006; Minchin & Nunn, 2014) but U. pinnatifida appears to be slower to invade these areas than man made structures (Farrell & Fletcher, 2006). However, as man made structures are an increasingly important proportion of coastal environments this species may still pose a significant threat to native biodiversity and is likely to spread extensively in Irish waters (Minchin & Nunn, 2014).




Undaria pinnatifida has a heteromorphic, diplohaplontic annual life cycle, with a diploid macroscopic sporophyte (kelp body) and a haploid microscopic gametophyte (Verlaque, 2007). Spores are released into the water and are viable for 5-14 days, though generally seem to settle within 10m of the parent plant (Forrest et al., 2000) and after settlement gametes are released.

There is a degree of conflicting information regarding the sea temperatures required for reproduction. Spore release is thought to begin when the water temperature exceeds 14 °C (Saito, 1975 in Farrell & Fletcher, 2006), however studies from the United States have found that recruitment is highest after periods of cold water (defined there as <15°C) and lower at higher temperatures (Thornber et al., 2004), suggesting there may be a narrow band of temperatures at which the species is capable of full reproductive output (~13°C) (Thornber et al., 2004). However it is thought to grow best in Europe at temperatures of below 12°C (Verlaque, 2007).

Pathway and vector description

As it was initially found in Belfast Lough and Carlingford Lough the most likely source of introduction is as a fouling organism on boats, as it is unlikely the species can survive transport in ship ballast water (Minchin & Nunn, 2014).

Long and medium range dispersal in Irish waters is likely to be predominately by leisure craft and movement of contaminated gear (Minchin & Nunn, 2014) and may occur at a rapid pace, e.g. in Argentina after being present in the country for approximately 15 years it was found to be spreading at a rate of 50km/year (Dellatorre et al., 2014).

Short range dispersal by natural means may show a lag phase between inoculation of an area and the spread of Undaria pinnatifida, as it took 7 years for it to spread from the marina to a nearby sea wall at Torquay marina (Farrell & Fletcher, 2006) though spread in New Zealand is thought to be at a rate of 100m/year (Forrest et al., 2000).

Mechanism of impact

Competition, Bio-fouling, Interaction with other invasive species, Other

Broad environment


Habitat description

Sublittoral rock and other hard substrates (EUNIS code A3).

Species group


Native region

Temperate Asia


World distribution(GBIF)

Irish distribution

Established - Localised. Originally found in Belfast Lough in 2012, it has been reported from Carlingford Lough in 2014 & is likely to spread further.

Native distribution

Native to Japan, China and Korea (Verlaque, 2007).

Temporal change

Date of first record category


Fifty year date category


Records submitted to Data Centre in 2023

The following map is interactive. If you would prefer to view it full screen then click here.

How can you help

Report any sightings to the National Biodiversity Data Centre.

Further information

See Speciea LAert poster for Japanese Kelp first issued in 2014: 

Delivering Alien Invasive Species In Europe (DAISIE) project list this as one of the 100 Worst Invaders in Europe. Invasive Species Specialist Group (ISSG) of the SSC- Species Survival Commission of the IUCN -International Union for Conservation Nature 100 Worst Invaders globally.



Casas, G., Scrosati, R., & Piriz, M. L. (2004). The invasive kelp Undaria pinnatifida (Phaeophyceae, Laminariales) reduces native seaweed diversity in Nuevo Gulf (Patagonia, Argentina). Biological Invasions, 6(4), 411-416.

Dellatorre, F. G., Amoroso, R., Saravia, J., & Orensanz, J. L. (2014). Rapid expansion and potential range of the invasive kelp Undaria pinnatifida in the Southwest Atlantic. Aquatic Invasions, 9(4), 467-478.

Farrell, P., & Fletcher, R. L. (2006). An investigation of dispersal of the introduced brown alga Undaria pinnatifida (Harvey) Suringar and its competition with some species on the man-made structures of Torquay Marina (Devon, UK). Journal of Experimental Marine Biology and Ecology, 334(2), 236-243.

Forrest, B. M., Brown, S. N., Taylor, M. D., Hurd, C. L., & Hay, C. H. (2000). The role of natural dispersal mechanisms in the spread of Undaria pinnatifida (Laminariales, Phaeophyceae). Phycologia, 39(6), 547-553.

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.

Thornber, C. S., Kinlan, B. P., Graham, M. H., & Stachowicz, J. J. (2004). Population ecology of the invasive kelp Undaria pinnatifida in California: environmental and biological controls on demography. Marine Ecology-Progress Series, 268.

Verlaque, M. (2007) Undaria pinnatifida. Global Invasive Species Database [Online].

CABI Datasheet

Global Invasive Species Database

DAISIE Factsheet