Biosecurity alerts: Carpet sea squirt

Page last updated: Friday, 17 March 2023 - 12:50pm

Carpet sea squirt (Didemnum vexillum) has been detected in Western Australia (WA) for the first time.

Carpet sea squirt (CSS) is a highly invasive marine invertebrate animal that has the potential to impact oyster and mussel aquaculture, marine environments, dive tourism industries as well as increasing maintenance costs for commercial and recreational vessels. 

A level 2 incident was declared on 25 January 2023 in response to the detection of CSS in WA and a Quarantine Area Notice was issued on 17 March.

Situation update

The aquatic pest has been detected in two locations in WA; Garden Island and at a marine facility in Henderson. The detection at Garden Island was the first confirmed detection in Australia.

DPIRD is working with the Australian Government Department of Defence (Defence) and the Department of Agriculture, Fisheries and Forestry (DAFF) to carry out surveillance and management activities. 

A Quarantine Area Notice (QAN) was issued on 17 March 2023 – please see the full notice, guidance document and map to the right of this page.

The Quarantine Area (QA) covers the waters adjacent to the Australian Marine Complex Common User Facility (AMC CUF) at Henderson South, encompassed by seawalls to the north and west, and extending 250 metres down the coastline south of the AMC CUF.

The aim of the QAN is to:

  • Manage the movement of vessels into the QA to minimise the spread of the pest.
  • Strengthen the requirements for biofouling inspections and treatments for vessels that regularly operate in the Quarantine Area or have been in the Quarantine Area for a period of six days or more.

There are no restrictions or requirements for vessels berthed for less than six days. The Quarantine Area covers waters that are typically restricted access waters, and recreational vessels should avoid the area.

DPIRD is also working with local stakeholders and Fremantle Port Authority to manage the incursion.

Key activities currently underway include:

  • Delimiting surveys to determine the spread of CSS.
  • Engagement with key stakeholders to raise awareness and undertake management activities.

About carpet sea squirt

CSS is native to east Asia, likely Japan, and has been introduced to New Zealand, North America and Europe. 

CSS is a marine invertebrate animal that can overgrow and smother native species. It can overgrow rocks, shellfish, sea sponges and man-made structures such as wharves, jetty pylons, pontoons, buoys and vessels. 

What can I do to prevent CSS from spreading in WA?

Recreational boaters, fishers and divers can assist in stopping the spread of marine pests and aquatic disease by keeping their boats, trailers, wetsuits and equipment clean. 

When you clean your equipment, make sure that any bait, debris and seaweed is removed. Check wheel arches on trailers, boat propellers, fishing tackle and footwear. Do not clean in the water or allow run off to enter the ocean. 

Use soapy water to clean your boat and trailer, fishing rods and other equipment, and allow them to dry completely before using them at another location, even if it is on the same day. 

There are many native species that look like carpet sea squirt so expert taxonomic identification and molecular techniques are required to confirm the species from DNA sequencing. 

If you find unusual marine species attached to vessels, sub-merged infrastructure or in the marine environment, report it to​

More information

carpet sea squirt factsheet and FAQ​ documents are available for download.

More detailed and technical information on CSS is found at the National Introduced Marine Pest Information System (NIMPIS​).​

Contact information

Phone 1800 815 507 (FishWatch 24-hour hotline)