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Black scar oyster (Magallana bilineata)

This introduced marine pest has been detected at several Far North Queensland locations since 2020. It can foul marine infrastructure and compete with native species for space, although its potential invasiveness and impacts are not yet well known.

Key facts

Type: Pest animal, invertebrate.

Native to: Western Pacific, from the Philippines to Tonga and Fiji.

Established in: QLD.

Other names: Crassostrea bilineata, Crassostrea madrasensis, Crassostrea iredalei, Philippine cupped oyster.

Identification

  • It is a large rock oyster with a variable oval or pear-shaped shell that can grow to 18 cm long.
  • The lower shell valve is deeper and cup-shaped, while the top valve has flat frills that can break off in dead shells.
  • The area inside the shell where the adductor muscle attaches is black.
  • It can be difficult to distinguish from native tropical rock oysters when young, before it reaches its distinctive larger size.
  • Look-alike: Native rock oysters are similar; black scar oysters can be distinguished by their larger size when mature and the black area inside the shell where the adductor muscle attaches.

Where it lives

In Australia it has been detected at Townsville, Mission Beach, Mourilyan Harbour, Cairns, Port Douglas, Cooktown and Elim Beach, in turbid, brackish intertidal or subtidal areas such as estuaries, bays, ports and harbours at depths of 0–16 metres.

Why it matters

  • It fouls submerged and floating infrastructure, including pylons, pontoons and boats.
  • It can foul wharf pylons, marinas and marine aquaculture farms.
  • It competes with native species for space.
  • Its potential invasiveness and impacts are not yet well known.

How it spreads

  • It has been detected in Townsville, Mission Beach, Mourilyan Harbour, Cairns, Port Douglas, Cooktown and Elim Beach.
  • It can attach to hard structures, including rocks, pylons, jetties and boat hulls.

Control methods

  • Regularly and thoroughly check and clean vessel hulls, including nooks, crannies and internal seawater systems.
  • Inspect, clean and dry equipment and gear, including pots, nets, fishing or diving gear, anchors and ropes, before moving to another location.
  • Report suspected marine pests and report any black scar oyster sighting within 24 hours online or by calling Biosecurity Queensland on 13 25 23.
  • It is a category 2, 3, 4 and 5 restricted marine pest under the Biosecurity Act 2014; do not move, keep, give away, sell or release it, and take all reasonable and practical measures under your control to minimise biosecurity risks.

Site hygiene and welfare

  • Check and clean boat hulls thoroughly, paying particular attention to nooks, crannies and internal seawater systems.
  • Inspect, clean and dry pots, nets, fishing or diving gear, anchors and ropes before moving them to another location.
  • Use methods set out in the national model codes of practice and standard operating procedures for the species.
  • Coordinate control with neighbours and the local government biosecurity plan, as isolated effort is quickly undone by reinvasion.

Classification by state

  • Australia (national): No national listing. Managed under state and territory law.
  • Queensland: Restricted matter, categories 2, 3, 4, 5. Report it to Biosecurity Queensland within 24 hours; do not give it away, sell or release it into the environment; do not move it; do not keep it. Everyone must also take all reasonable and practical steps to minimise its risks (the general biosecurity obligation).
  • New South Wales: General biosecurity duty. Not prohibited matter in NSW. 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: Not declared. Not declared under the Landscape South Australia Act 2019. Other laws may still apply.
  • Western Australia: Not listed. Not found in the Western Australian Organism List. Check with DPIRD before moving or keeping it.
  • Tasmania: Not a declared pest. Not a declared pest or prohibited matter in Tasmania. Importing animals is still controlled by Biosecurity Tasmania.
  • Northern Territory: Not a declared pest. Not on an NT declared or prohibited list. Check with the NT Government before keeping, moving or releasing 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)

Sources