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Wakame (Undaria pinnatifida)

Wakame is an introduced marine seaweed found in Tasmania and Victoria, where it can form dense stands. It can compete with native species for light and space, and foul marine infrastructure.

Key facts

Type: Weed, aquatic.

Native to: Japan, China and Korea.

Established in: VIC, TAS, SA.

Other names: Undaria Seaweed, Japanese Seaweed, Japanese Kelp.

Best time to act: The conspicuous sporophyte is usually present from late winter to early summer.

Identification

  • A golden-brown kelp that grows 1–3 metres high.
  • It has a holdfast, a cylindrical stipe and a flattened, branched blade.
  • The stipe extends through the blade as a distinct midrib, up to 3 cm wide.
  • Fertile plants have frilly, spore-bearing sporophylls on the stipe.
  • Look-alike: The native common kelp (Ecklonia radiata) is similar, but Wakame has a distinct midrib and, when reproductive, a frilly sporophyll surrounding the stipe.

Where it grows

In Australia, Wakame occurs on the east coast of Tasmania and in several bays in Victoria, growing on hard surfaces from the intertidal zone to depths of about 20 metres.

Why it matters

  • It can form dense forests that compete with native species for light and space, potentially excluding them.
  • It fouls marine infrastructure, including vessel hulls and aquaculture structures.

How it spreads

  • Wakame is thought to have spread to and within Australia primarily by hull fouling, attached to ships travelling from infected areas.
  • It was first sighted in Tasmania in 1988, although it may have been present since 1982, and was discovered in Port Phillip Bay, Victoria, in 1996.
  • It could spread to other areas based on its wide temperature tolerance.

Control options

  • Wakame can only be controlled by physical removal, although this is largely unsuccessful.
  • Chemical biocides have been trialled, but made no appreciable impact and are labour intensive.

Hygiene and washdown

  • Hull fouling is a known spread pathway: Wakame can be transported attached to ship hulls.
  • It also fouls vessel hulls and aquaculture structures.
  • Inspect and clean vehicles, plant and footwear before leaving an infested area, paying attention to tyres, radiators, belly plates, tracks and floor mats.
  • Wash down at a designated bay where runoff is contained and can be monitored for seedlings.
  • Record each washdown so the client has evidence of clean entry and exit.

Classification by state

  • Australia (national): Priority marine pest. On the Australian Priority Marine Pest List, agreed by all governments as a marine pest of national concern.
  • Queensland: Prohibited matter. Report it to Biosecurity Queensland on 13 25 23 within 24 hours and do not move or deal with it. Everyone must also take all reasonable and practical steps to minimise its risks (the general biosecurity obligation).
  • New South Wales: Notifiable aquatic pest. It must not be possessed, bought, sold, moved or released in NSW, and you must notify NSW DPIRD within one working day of finding it. The general biosecurity duty applies: anyone dealing with it must prevent, eliminate or minimise the risk it poses.
  • Victoria: Noxious aquatic species. Declared a noxious aquatic species under the Fisheries Act 1995, so it must not be brought into Victoria, kept, sold, moved or released into waters. Report any sighting to the Victorian Fisheries Authority on 13 FISH (13 3474).
  • South Australia: Noxious species. Declared a noxious species under the Fisheries Management Act 2007, so it must not be brought into South Australia, kept, sold or released, and it must not be returned to the water alive. Report any sighting to PIRSA FISHWATCH on 1800 065 522.
  • Western Australia: Noxious fish. Prescribed as a noxious fish under the Fish Resources Management Regulations 1995, so it must not be brought into WA, kept, sold or released. Report any sighting to FishWatch on 1800 815 507.
  • Tasmania: Declared weed. Property managers are required by law to control declared weeds, and their import and sale are prohibited.
  • Northern Territory: Not declared. Not on the NT A to Z weed list, and Weeds Australia does not list it as declared in the NT. Check the NT declared weeds list before moving or planting it.
  • Australian Capital Territory: Not declared. Not declared under the Biosecurity Act 2023 (ACT). A general biosecurity duty still applies.

Legal obligations

Every state and territory places a duty on landholders and people working on land to prevent the spread of invasive species, such as the general biosecurity obligation in Queensland and the general biosecurity duty in New South Wales. Declarations and control requirements differ between states and local government areas, so check the current official list before work starts.

  • Victoria: Catchment and Land Protection Act 1994 (Vic), administered by Agriculture Victoria
  • Tasmania: Biosecurity Act 2019 (Tas), administered by Biosecurity Tasmania
  • South Australia: Landscape South Australia Act 2019 (SA), administered by the regional landscape board

Sources