Wakame Watch


Wakame (Undaria pinnatifida) is a large species of seaweed originating from the Pacific and is considered by the IUCN Invasive Specialist Group to be one of the 100 'world's worst' invasive species, due to its potential to impact ecological and economic interests. Scientists do not currently believe that the true spread of the species is known for Great Britain and North West Europe and producing an accurate distribution of this species is important in terms of managing and controlling spread. Wakame Watch was established in order to generate an up-to-date picture of the distribution of the species, by encouraging recording of sightings from the public, in particular, we are asking divers, snorkelers, recreational boat users, fishermen and environmental surveyors to let us know when they encounter the species.


Image: Keith Hiscock (All rights reserved)

Image: John Bishop (All rights reserved)

Image: John Bishop (All rights reserved)



Wakame is relatively easy to identify with a little knowledge of its key features. When submitting records, please include photographs clearly showing as many of these key features as possible.

Key features (sporophytes)

  • Dark green - brown colouration
  • A distinct midrib
  • A claw shaped/ branching holdfast
  • Fairly thin, membranous, sometimes crinkled frond
  • Frond branches (more so in mature sporophytes) almost like a Christmas tree - may appear as serrations at the base of the frond in young individuals
  • Corrugated ruffle shaped reproductive structure at the base of the stipe (except in young individuals)
  • May grow as long as 3 metres

ID Terms

  • Blade-the leaflike part of a seaweed
  • Digitate-shaped like a spread hand
  • Frond-the erect part of a seaweed including stipe and blade
  • Holdfast- the attachment structure that anchors a macroalgae to the substratum, can take a number of different forms such as rootlike, a disc (discoid), claw like or bulbous.
  • Membranous-forming a thin layer, may be semi-transparent, often sheet-like.
  • Midrib-a strengthened vein running along the middle of the frond
  • Stipe-stalk like part arising from the holdfast and connecting to the blade
  • Sporophyte-the spore producing phase in the life-cycle of plants with alternating generations. For the algae described the sporophyte is the large macroalgae observed on the shore, the gametophyte phase is microscopic.
  • Sporophyll-reproductive body producing gametophytes
  • Thallus-the entire body including the holdfast, stipe and blade.

Similar Species

Dabberlocks (Alaria esculenta)


Image: Bernard Picton (CC-BY, published on iNaturalist)

  • Long narrow, oval shaped frond (not 'branching')
  • Reproductive lobes at base and no reproductive frills

Sugar kelp (Saccharina latissima)


Image: Bex Goreham (CC-BY, published on iNaturalist)

  • No midrib
  • Stipe is thin and smooth
  • Frond long and undivided
  • No sporophylls at base of stipe

Furbellows (Saccorhiza polyschides)


Image: Noa (CC-BY, published on iNaturalist)

  • Knobbly, bulbous holdfast
  • No midrib
  • Hand shaped frond
  • Flattened stipe

Broad Leaf Weed (Petalonia fascia)


Image: Michael G. Shepard (CC-BY-NC, published on iNaturalist)

This seaweed may be confused with the juvenile stage of Wakame

  • No midrib
  • Colour is brown rather than greenish.
  • Stipe is smooth (no corrugations at base of frond)
  • Holdfast is discoid rather than claw like
  • Up to 40 cm long

Other Kelps (Laminaria digitataLaminaria hyperboreaLaminaria ochroleuca)

These large brown seaweeds may be distinguished from Wakame by the following characteristics.

  • No midrib
  • Darker brown in colour than Wakame, although Laminaria ochroleuca is yellowish in parts
  • Blades are digitate (branching into ‘fingers’ hand shaped rather than Christmas tree shape of Wakame)
  • Fronds are leathery and thicker than Wakame
  • Stipe thickness means plants may be erect rather than lying flat when uncovered
  • No sporophylls at base of stipe

Submit a Record

If you find Wakame, a sighting report requires:

  •  A clear photograph
  •  The exact location, time and date of the sighting

To help confirm that the seaweed is Wakame, use the identification aid above.

To report the sighting:

  • If you have the iNaturalist app (available on iOS and Android), a useful tool to record any wildlife sightings both in the UK and overseas, you can submit the record directly on the app or via the iNaturalist website.
  • You can also upload records to iRecord, which like iNaturalistUK, shares the data with the NBN Atlas, a national biodiversity database.
  • Alternatively, you can email the Marine Biological Association through dassh.enquiries@mba.ac.uk with your photograph, location, time and date of the sighting and they will record the sighting for you.


Project Sponsors

The Wakame Watch project was sponsored by Global Ocean - a marine conservation charity based in London that aims to educate and raise awareness about the importance of healthy oceans for sustaining life, through engaging the public in ways to contribute positively to stewardship of our blue planet. Their objective is to inspire changes in attitude and behaviour towards our marine environment through developing key campaigns, organising events to raise awareness, supporting similar organisations in their mission and providing free educational workshops and resources for schools and the public. They currently run our primary campaigns across the UK, India, UAE and US centred on various marine conservation issues.

Further Information

For more information see the GB Non-Native Species Secretariat (NNSS)