Q: What is Caulerpa taxifolia?
A: Caulerpa taxifolia is a bright green seaweed with main stems that can grow up to three metres long with up to 200 fronds growing off them that look like feathers or ferns. It can live as individual plants or grow to form dense blankets covering large areas of riverbed. It can grow up to 25mm a day and spreads vegetatively – by itself. New infestations can start from small fragments. It’s a tropical species and some strains are native to the warm waters of northern Australia. It has been nominated as one of the world’s worst invasive species. Getting the weed caught in anchors, fishing lines and other equipment and then reintroducing these items into new waters without cleaning the weed off can easily spread the weed.

Q: Where and when was it found in South Australia?
A: Caulerpa taxifolia was found in West Lakes and the area of the Port River near the Jervois Bridge in March 2002. The State Government immediately investigated the situation and conducted trials to find out what would kill the weed. Fishing bans and recreational restrictions were implemented in West Lakes and fishing bans were implemented near the Jervois Bridge. An eradication strategy involving fresh water in West Lakes was implemented from July to December 2003. Following eradiction of the weed in West Lakes, fishing bans and recreational restrictions were lifted. For the Port River, salt, black plastic and chlorine as well as suction methods have been used. Further infestations were found in the Port River in early 2004 and fishing bans were extended to the Garden Island areas of the Eastern Passage/Barker inlet. Following discoveries of the weed’s spread in May/June 2005 the State Government has implemented a control strategy and lifted the fishing bans that covered only some areas of infestation. Anchoring bans have been placed on all waters of the Port River south of an east west line from Snapper Point to Torrens Island and all waters of the North Arm, Eastern Passage, Angas Inlet, Torrens Reach and Barker inlet south of a east-west line passing through Middleground Beacon. A map of the area is on this website.

Q: What is the current extent of infestation
A: The map available on this website details the infestation as at June 2005.

Q: Why is it bad?
A: Caulerpa taxifolia has the potential to spread over large areas, and it will exclude native species such as sea grasses. Where it invades and pushes out native flora, it destroys habitat for fish, especially nurseries, meaning they can no longer find food and breeding grounds. Fish do not eat it because it contains a toxin that makes it distasteful to them. It has the potential (based on its known depth and temperature ranges, and invasive history) to spread over most South Australian waters including Gulf St Vincent and Spencer Gulf.

Q: How long does it survive out of water – for example on an anchor chain?
A: Probably about 10 days but possibly up to two weeks in the right conditions. It can survive on fishing, boating and diving gear, so if a even a small piece is caught in your gear and you fish somewhere else next time, the Caulerpa taxifolia may be able to start a new infestation.

Q: Is it safe to pick up?
A: Yes, it’s perfectly safe to pick up. While it does contain a toxin, it’s one that makes it distasteful to fish, which helps it to survive and spread.

Q: Is it harmful to humans?
A: It is not dangerous to people unless consumed in large quantities. You should not be poisoned from contact with it or through accidental consumption of small amounts, eg while swimming.

Q: Is there any still in West Lakes?
A: No, the area of the lakes is clear of the weed and has been since December 2003 because of the freshwater treatment by PIRSA in mid-2003. But PIRSA monitors the lakes and the public are asked to remain vigilant and report any sightings to FISHWATCH on 1800 065 522.

Q: How does it spread?
A: It spreads by growth from its stolons (long stems) and can also form a new plant from a fragment broken off an existing plant. A new plant can form from a tiny fragment and can survive out of the water for 10 days or more, for example on boots, fishing tackle, or an anchor chain.

Q: Why does it have to be disposed of in a bag?
A: Because it can survive out of the water for 10 days or longer and disposing of it carelessly might mean it ends up back in the water, where it will infest a new area. Putting it in a sealed, biodegradable bag, like the type used to pick up a dog’s droppings, and putting it in a bin ensures the weed can’t be returned to the water.

Q: How did it get into these parts of the river?
A: The long, warm summer of 2004–05 and mild start to the winter provided Caulerpa taxifolia with perfect conditions to spread. It takes only a fragment to start a new infestation, which is why people are asked to pick up, bag , and dispose of any they find on their fishing gear, anchors or boats.

Q: What is the risk of it getting into Gulf St Vincent and what might help it get there?
A: There are lots of ways it can move, including tides and currents. Disturbing the weed and breaking it off and other factors can have an effect. Fishers and other recreational users of the waterways can move it by allowing small amounts to be transported from one place to another inadvertently leaving it on fishing gear, anchor chains etc.

Q: What should people do if they see Caulerpa taxifolia in the river or the Gulf?
A: Everyone boating, fishing or taking part in any water sport should be vigilant and report a sighting to FISHWATCH on 1800 065 522 wherever they find it. To make sure you know what it looks like, a pamphlet entitled Identifying Caulerpas in South Australian Waters is available from PIRSA and is posted on this website. People who see the weed should note the location, date of siting, water depth (if possible), type of siting (while diving, on an anchor chain, from the shore), whether it was isolated or a big patch, and your contact details.

Q: Is there any Caulerpa taxifolia already in the Gulf – or – is any survey work being carried out in the Gulf to identify Caulerpa taxifolia?
A: The weed has not been found growing in the Gulf. Everyone using the Gulf, whether for recreation or commercial fishing is urged to be vigilant and report a sighting to FISHWATCH on 1800 065 522 with details of the location, date of siting, water depth (if possible), type of siting (while diving, on an anchor chain, from the shore), whether it was isolated or a big patch, and your contact details.

Q: Where did it come from?
A: Caulerpa taxifolia is native to Queensland and other tropical areas. An invasive strain escaped from an aquarium and was discovered in the Mediterranean in 1984. The species has become established and is considered a pest in New South Wales. We don't know how it was released in West Lakes but it may have established from a released aquarium specimen.

Q: Has it caused problems elsewhere?
A: Yes, problems have occurred from outbreaks of this pest species in places as far apart as the Mediterranean, Californian coast and several estuaries and inlets on the NSW coast. Between 1984 and 1997, 99 invaded sites were found around the world totalling more than 4600 hectares.

Q: When did it first appear in South Australia?
A: It was first discovered in West Lakes in March 2002 and subsequently found in the upper Port River.

Q: How can people using the river for recreation recognise Caulerpa taxifolia?
A: You can check this website and a pamphlet Identifying Caulerpas in South Australian waters is available from PIRSA that gives colour photographs of Caulerpa taxifolia and its harmless relatives. If you do not have a copy and cannot be sure, it’s best to be safe rather than sorry and dispose of what you find in a sealed, biodegradable bag.

Q: What is PIRSA doing about it?
A: PIRSA is undertaking targeted fringe control of infested areas, especially where there is known to be a higher risk, such as near boat moorings, around the Torrens Island power station warm water outlet, where tides and currents might deposit it. PIRSA is also creating risk mitigation plans for construction and dredging sites, such as near the port redevelopment and the opening bridges. Anchoring bans have been placed on all waters of the Port River south of an east west line from Snapper Point to Torrens Island and all waters of the North Arm, Eastern Passage, Angas Inlet, Torrens Reach and Barker inlet south of a east-west line passing through Middleground Beacon. A map of the area is on this website. A major public education campaign will be carried out to inform everyone using the waterway of the problem and how they can help.

Q: Is it dangerous to the dolphins?
A: No. However as the weed is a threat to fish habitats by taking over areas of habitat and displacing fish, all efforts must be made to stop the spread of the weed to ensure fish are available for dolphins to eat.

Q: Why have fishing bans been lifted in the Port River when fishing and boating may disturb the weed?
A: Due to the extent of the spread, banning fishing in one or two small areas is not the answer. Many people fish in the Port River and not all observe bans. It will be more effective to make people aware of the environmental problem and what they can do to help stop the spread of the weed. Anchoring bans have been placed on all waters of the Port River south of an east west line from Snapper Point to Torrens Island and all waters of the North Arm, Eastern Passage, Angas Inlet, Torrens Reach and Barker inlet south of a east-west line passing through Middleground Beacon. A map of the area is on this website. If people do the right thing by inspecting anchors, ropes and fishing tackle and make sure that any fragments are not returned to the water, we can all help save our fishing grounds for the future. At the same time, the State Government will continue to kill patches of the weed as part of the control effort. PIRSA Fisheries still has the power to prosecute people who deliberately throw weed back into the water.