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Red sea lettuce (Grateloupia turuturu)

Red sea lettuce is an introduced marine alga recorded in Tasmania and Victoria, including in coastal waters and harbours. It can establish and spread on natural and artificial surfaces, so recognising it and preventing its movement on boats and equipment are important biosecurity measures.

Key facts

Type: Weed, aquatic.

Native to: Northwest Pacific, including coastal waters of East Asia.

Established in: NSW, VIC, TAS, SA.

Other names: Red-tongue weed, Devil's tongue weed, Japanese seaweed.

Best time to act: Survey regularly and treat only when the alga is readily visible and conditions allow safe, contained removal.

Identification

  • Look for a red, reddish-purple or brownish-red seaweed with broad, flat, leafy blades.
  • The blades are usually soft and slippery, with irregularly shaped or wavy edges.
  • A blade may be broad and lobed, and narrows towards a short stem-like attachment to the surface.
  • It attaches to rocks or other hard surfaces by a small holdfast.
  • Large, developed fronds can be conspicuous among other seaweeds on harbour structures and shorelines.
  • Look-alike: Other red seaweeds can also have broad, flat blades, and colour or shape alone may not reliably distinguish them.
  • Look-alike: For uncertain specimens, photograph the whole plant and its attachment point and seek identification from a marine algae specialist or the state biosecurity agency.

Where it grows

In Australia it has been recorded in coastal waters of Tasmania and Victoria, where it can grow on hard surfaces in sheltered bays, harbours and other coastal sites.

Why it matters

  • It can establish and spread in coastal waters, including on artificial structures such as harbour infrastructure.
  • Dense growth may compete for space with native seaweeds and other organisms attached to the same surfaces.
  • Its potential to affect native communities is a concern where it spreads from sheltered or modified sites to natural rocky habitats.
  • The scale of its ecological and economic impacts in Australia has not been clearly demonstrated.

How it spreads

  • It can spread when fragments or reproductive material reach new suitable surfaces.
  • Boats, hull fouling, anchors and other marine equipment can carry attached algae or fragments between sites.
  • Movement of contaminated aquaculture, construction or other marine equipment may also transfer it.

Control options

  • Report suspected new occurrences to the relevant state or territory biosecurity agency and seek advice before disturbing the algae.
  • For an authorised removal, work carefully to collect the whole alga and loose fragments, preventing them from drifting or washing back into the water.
  • Securely contain and dispose of removed material as directed by the responsible authority; do not use herbicides unless a product and application are specifically registered and authorised for that marine use.
  • Revisit treated sites and nearby surfaces to check for regrowth or missed fragments, and follow the agency's instructions for further action.

Hygiene and washdown

  • Before moving a boat or marine gear, inspect and remove attached algae and fragments, keeping all removed material contained and out of the water.
  • Clean gear and equipment at the site where practical, and do not transfer rinse water, algae or contaminated material to another waterway.
  • 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): No national listing. Managed under state and territory law.
  • 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: Not declared. Not declared under the Catchment and Land Protection Act 1994. Other Victorian laws may still apply.
  • 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: Not declared. Not a declared weed in Tasmania. Other laws may still apply.
  • Northern Territory: Check NT list. There is no NT weed profile for it. Check the NT declared weeds list for its current status.
  • 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.

  • New South Wales: Biosecurity Act 2015 (NSW), administered by NSW Department of Primary Industries and Regional Development
  • 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