Carpet sea squirt (CSS) is an introduced marine pest in Australia. The pest is also known as invasive colonial sea squirt or sometimes as 'sea snot' or 'sea vomit'.
CSS overgrows and smothers native marine species such as shellfish, sea sponges and algae. It fouls vessels, marine infrastructure, and aquaculture stock and equipment.
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Detection in Australia
Carpet sea squirt has been detected in both Western Australia and New South Wales.
The first detection was in April 2021 at HMAS Stirling, Garden Island, WA. In January 2023, CSS was also detected at the Australian Marine Complex (AMC) in Henderson, WA.
In May 2023, CSS was detected in NSW at Fleet Base East (FBE) in Sydney Harbour.
Response program
The lead agency for each state response varies based on the location. Some detections are at Defence sites. At these locations, many agencies work together on the response.
The Consultative Committee on Introduced Marine Pest Emergencies (CCIMPE) provides technical advice on each response. CCIMPE includes marine pest managers from Australian, state and territory governments.
CCIMPE has recommended that it is not technically feasible to eradicate CSS.
Western Australia
Response at HMAS Stirling
The Department of Defence is leading the response at HMAS Stirling, as this is a Commonwealth site. It is working with:
- Western Australian Department of Primary Industries and Regional Development (DPIRD)
- Australian Government Department of Agriculture, Fisheries and Forestry (DAFF).
CCIMPE agreed that it is not technically feasible to eradicate CSS at HMAS Stirling. Response activities include:
- delimiting surveys to show the extent of the pest colonies
- ongoing marine pest surveillance and monitoring
- Defence has implemented a nationally aligned vessel management plan to prevent spread of CSS.
Targeted control and removal of CSS colonies from marine infrastructure at HMAS Stirling has been unsuccessful in eradicating this pest.
Response at the Australian Marine Complex
DPIRD leads the response to the detection at the AMC in Henderson, WA.
Response activities include:
- completion of delimiting surveys to show the extent of the pest colonies
- ongoing marine pest surveillance at Port of Fremantle and in Cockburn Sound
- putting in place a Quarantine Area Notice (QAN) at the AMC, Henderson.
- targeted control and removal of colonies on vessels in the QAN.
- extra vessel management procedures and monitoring to prevent spread.
DPIRD is continuing its surveillance program with WA Port Authorities. The program provides marine pest surveillance at 10 ports in WA. DPIRD is working with local stakeholders and the Fremantle Port Authority.
New South Wales
The Department of Defence is leading the response at Fleet Base East (FBE) in NSW. It is working with:
- NSW Department of Primary Industries (DPI)
- Department of Agriculture, Fisheries and Forestry (DAFF).
Response activities include:
- Defence has implemented a nationally aligned vessel management plan to prevent spread of CSS
- delimitation has identified that while not extensive, CSS appears to be established across FBE, where it is unlikely to be able to achieve eradication or containment.
See more
How we coordinate our response to outbreaks.
Your obligations
Follow these steps to help stop the spread of CSS.
Report sightings
Report anything unusual, even if you’re not sure.
Contact the relevant state or territory to report a marine pest sighting.
Keep your gear clean
Recreational boaters, fishers and divers should follow the check, clean, dry method. This means:
- Check wheel arches on trailers, boat propellers, fishing tackle and footwear for bait, debris and seaweed.
- Keep your boats, trailers, wetsuits, fishing rods and equipment clean. Use soapy water.
- Allow your boat and trailer, fishing rods and other equipment to dry completely before using them at another location.
Follow the rules
Keep exotic pests and diseases out of Australia. Never ignore our strict biosecurity rules.
Foreign warships are requested to comply with Australian Government requirements to enter Australian waters.
Check requirements for military vessels arriving in Australia.
Restrictions in Western Australia
WA has issued a quarantine area notice (QAN).
The quarantine area in WA covers the waters near the Australian Marine Complex at Henderson South. This includes seawalls to the north and west and 250 metres south down the coastline.
Vessels that operate in the quarantine area must be regularly treated and inspected.
Check the quarantine area and vessel procedures in WA.
About the pest
CSS is an invasive marine animal. It can overgrow rocks, shellfish, sea sponges and algae. It covers man-made structures such as wharves, jetty pylons, pontoons, buoys, and vessels.
The pest is native to East Asia. It has been introduced to New Zealand, North America, and Europe.
CSS is listed on the National priority List of Exotic Environmental Pests, Weeds and Diseases.
See more technical information about CSS (National Introduced Marine Pest Information System).
What to look for
Carpet sea squirt is usually a yellow grey mass, but the colour can vary. CSS is a filter feeder and not a predatory animal. It’s covered with holes that siphon water to feed on small phytoplankton and organic matter.
CSS grows fast and aggressively. It can thicken up to 10cm. CSS produces ‘arms’ or tendrils up to 1m long that hang below the main mass.
Photo courtesy of C. Woods, NIWA
How it spreads
CSS reproduces both sexually and asexually. New colonies can grow from small fragments that break off from larger colonies.
CSS is transported to new locations as biofouling on vessels, or sometimes from natural dispersal through ocean currents.
What it impacts
CSS impacts oyster, mussel and finfish aquaculture, marine environments, vessel maintenance and dive tourism industries.
The pest clogs nets, bags or ropes mainly used to contain shellfish. Buoys and ropes can become weighed down with colonies. It also attaches itself to infrastructure and vessels.
CSS infestations lead to increased cost and reduced income for aquaculture industries. It also increases costs of cleaning vessels and marine infrastructure.