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Aquarium caulerpa (Caulerpa taxifolia)

The invasive strain is established in New South Wales and South Australia, where it can form large beds and smother native marine life. It is difficult to distinguish from widespread, non-invasive Caulerpa taxifolia without genetic testing.

Key facts

Type: Weed, aquatic.

Native to: Thought to be native to southern Queensland; the invasive strain is likely to have originated in Queensland..

Established in: QLD, NSW, SA, WA.

Other names: Caulerpa, Green Macroalga.

Identification

  • This is a green marine alga with creeping stems that meander across the seabed.
  • Upright, flattened fronds grow from the creeping stems and are about 20 to 60 cm tall.
  • The fronds have small, slightly flattened, sickle-shaped branchlets that grow in one plane.
  • There is a slight constriction at the base of each branchlet and a small gap between adjacent branchlets.
  • The invasive strain cannot be reliably distinguished from non-invasive Caulerpa taxifolia by appearance alone.
  • Look-alike: Caulerpa mexicana has a flat midrib, while Caulerpa taxifolia has a compressed midrib.
  • Look-alike: Caulerpa sertularioides has cylindrical branchlets, while Caulerpa taxifolia has flat ones; Caulerpa scalpelliformis has alternate branchlets, while Caulerpa taxifolia has opposite branchlets.

Where it grows

In Australia it occurs in marine waters, including New South Wales, Queensland and South Australia, growing on rock, sand, mud and seagrasses, usually at depths of 3 to 35 m.

Why it matters

  • It can smother other algae, seagrasses and sessile invertebrate communities.
  • It competes with native species for nutrients and light and can also affect them through secreted caulerpenyne compounds.
  • Large single-species beds can reduce native species diversity and affect fish habitats.

How it spreads

  • It can be spread through the aquarium trade, including escaped aquarium specimens and the dumping of aquarium water or materials.
  • Small fragments can grow into new plants, and local spread also occurs through vegetative growth of the stems.
  • It may spread to new areas by attaching to ship hulls or on infected recreational equipment.

Control options

  • Mechanical removal can be used for small outbreaks.
  • Coarse sea salt has rapidly killed the seaweed in New South Wales, although effectiveness varied between sites.
  • Chlorine poisoning has been used for small infestations, including infestations covered with black plastic tarpaulins.
  • Check current approved methods and registered herbicides with the relevant authorities before treatment.

Hygiene and washdown

  • Do not dump aquarium water or materials into the marine environment, as aquarium maintenance and disposal can spread the alga.
  • Avoid transferring fragments on boat hulls or recreational equipment from infested areas.
  • 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: 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. This applies in any area of the State except in the Pilbara and Kimberley Region. 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.

  • Queensland: Biosecurity Act 2014 (Qld), administered by Biosecurity Queensland (13 25 23)
  • New South Wales: Biosecurity Act 2015 (NSW), administered by NSW Department of Primary Industries and Regional Development
  • South Australia: Landscape South Australia Act 2019 (SA), administered by the regional landscape board
  • Western Australia: Biosecurity and Agriculture Management Act 2007 (WA), administered by the WA Department of Primary Industries and Regional Development

Sources