Introduction

Caulerpa taxifolia (Caulerpa) is a fast growing seaweed that is native to tropical Australia and the South Pacific that has colonised various areas outside its natural range, including several NSW waterways. Caulerpa was first found in NSW in April 2000, and it has now been detected in 14 NSW estuaries and lakes and one small oceanic population.

In the past, Caulerpa has been widely used as a decorative plant in the NSW marine aquarium trade. This seaweed can invade cool temperate waters, and Caulerpa has become established in several countries and areas outside its natural range.

Caulerpa is a Class 1 noxious species in all NSW waters under the Fisheries Management Act 1994. It is illegal to possess or sell the seaweed; and fines of up to $11,000 apply. The noxious listing also provides NSW DPI with the power to seize and destroy Caulerpa, or require its destruction.

The invasive nature of Caulerpa has raised concerns as it has the potential to grow rapidly, alter marine habitats and affect biodiversity.

Aquatic pests, including Caulerpa are usually extremely difficult to eliminate once they have become established in the wild. It is therefore important to prevent noxious species such as Caulerpa from entering new waterways.

Natural distribution & biology

Caulerpa is a green alga with regularly-spaced feather-like fronds growing along a running stolon that is attached to the substrate. The fronds vary in length, and have been reported to reach a maximum of 30 cm in NSW waters.

Caulerpa is native to tropical regions throughout the world, including tropical and subtropical parts of Australia, with its southern natural limit at Moreton Bay in Queensland.

Caulerpa was first identified outside its natural range near Monaco in the Mediterranean Sea in 1984. It was dubbed the aquarium strain as it was believed to have been accidentally released from aquariums. It has since colonised thousands of hectares in the Mediterranean from France to Croatia (although some populations have experienced dieback in recent years) and has also colonised two locations in California.

Caulerpa can tolerate low temperatures and NSW researchers have confirmed that it can survive out of water, in moist conditions, for up to 3 days. It can colonise most kinds of substrates including rock, sand, mud and seagrass beds. In NSW, it has been found in depths ranging from less than 1 m to 12 m and is capable of rapid growth.

Reproduction of Caulerpa outside its natural range is asexual and dispersal occurs through fragmentation. It has been demonstrated in laboratory experiments that a fragment as small as 1 cm can settle and start growing. Growth rates are greatest in the warmer months and lowest during winter.

Where is it in NSW?

Caulerpa was first identified in NSW during April 2000 in Port Hacking, 30km south of Sydney.

Important note: These maps are indicative only and may contain errors and omissions. They are based on surveys of areas where Caulerpa taxifolia (Caulerpa) has been known to occur or has been reported, not on comprehensive surveys of the entire waterway. Thus, Caulerpa taxifolia may occur in additional areas not shown on the maps. In addition, the distribution of Caulerpa can change markedly over time, either expanding or contracting (for example, it often dies off during winter and grows rapidly in summer). The maps show where Caulerpa has been found at some point in the period specified in each particular location. NSW DPI and its employees disclaim liability for any act done on the basis of information from this map and any consequences of such acts or omissions. Report any new sightings or changes in the distribution of Caulerpa taxifolia by calling our 24 hour hotline, 02 4916 3877.

This invasive seaweed has since been identified in the following locations:

• Batemans Bay  328.8 kb
  
• Botany Bay  495.8 kb
  
• Brisbane Waters  447.8 kb
  
• Burrill Lake  354.2 kb
  
• Durras Lake  331.2 kb
  
• Lake Conjola  355.4 kb
  
• Lake Macquarie (considered Caulerpa free as at February 2009)  446.7 kb
  
• Narrawallee Inlet  260.6 kb
  
• Hawkesbury River (Patonga)  258.0 kb
  
• Pittwater  414.1 kb
  
• Port Hacking  405.7 kb
  
• Port Jackson  435.4 kb
  
• St Georges Basin  320.2 kb
  
• Wallagoot Lake  148.5 kb
  

How did it get here?

The origin of the NSW populations is unclear, but the seaweed is likely to have been introduced from an aquarium release, for example by cleaning tanks and disposing of unwanted weed into a waterway.

After arriving in NSW, Caulerpa seems to have been spread among estuaries by fishing and boating activities. Fragments can get caught up in fishing gear, diving equipment and boats, and are easily spread to other areas or waterways as they can survive for two to three days out of water.

What are its impacts

Since Caulerpa was first discovered in NSW in 2000, studies have been undertaken to determine the effects of the seaweed on aquatic ecosystems. There are two key characteristics of Caulerpa that have caused significant concern and may have helped Caulerpa to establish and spread in areas outside its natural range. Firstly, Caulerpa has rapid growth, leading to concerns it could out-compete native seagrass. Small fragments of Caulerpa can grow into new plants and create large colonies. Research results to date from NSW indicate that dense seagrass beds are relatively resistant to invasion from Caulerpa, however, sparse seagrass beds (Zostera in particular) may be at risk from Caulerpa.

The numbers of and species of fishes have been found to vary between Caulerpa and native seagrass. Specifically, Caulerpa supports far fewer seahorses than do seagrasses, while there are more gobies in Caulerpa.

Research focussing on the impacts of Caulerpa on invertebrates living in and on sediments has found that the cockle Anadara trapezia recruits in greater numbers to Caulerpathan to seagrass or unvegetated areas, but that the survival and reproductive output of females cockles is less in Caulerpa. These observed impacts on invertebrates appear to be as a result of low levels of oxygen in water under the Caulerpaand in the sediments. 

What is NSW DPI doing?

From 2001, the NSW Government developed a comprehensive control program for Caulerpa.

The program has included the removal of the weed from sale in the aquarium trade, controlling infestations in high priority areas, educating the public and restricting the use of fishing gear by implementing fishing closures to help stop the weed spreading.

NSW DPI has trialled a variety of control methods, including dredging, smothering and applying salt and determined that for smaller infestations salt treatment is the most efficient control method. When swimming pool salt is put on Caulerpa the salinity rises to a point where the weed is killed in a matter of hours. A major limitation to the technique, because Caulerpa reproduces asexually from tiny fragments, is that salting needs to kill all fragments in order to eradicate the seaweed. Large outbreaks are almost impossible to eradicate and therefore it is of primary importance to prevent any further spread of Caulerpa to new locations. The application of salt also negatively impacts Posidonia, a native seagrass, and so it is not possible to apply salt to Caulerpa which invades Posidonia beds.
NSW DPI continues to survey a range of estuaries along the coastline, particularly areas north and south of infested estuaries such as Lake Macquarie and Burrill Lake. These surveys resulted in the discovery of Caulerpa in both Batemans Bay in February 2007, and Durras Lake in April 2007.

NSW DPI has established long term monitoring plots in several estuaries to assess the impact of the seaweed on native seagrasses and we are also monitoring the rate of spread of known populations.

NSW DPI is also supporting research by universities to investigate the potential impacts of Caulerpa on fishes, invertebrates and nutrients in sediments.

• NSW Control Plan for Caulerpa taxifolia
  The Control Plan has been reviewed and updated to reflect the latest research findings.

Caulerpa taxifolia in Wallagoot Lake - Case Study - updated November 2009

Executive Summary

Caulerpa taxifolia (Caulerpa) is a noxious marine alga native to tropical Australia. The weed is naturally cold tolerant and has been discovered in 14 estuaries in NSW and one oceanic location at Merri Reef. It has also been discovered in waterways in South Australia.

The most recent discovery of Caulerpa was confirmed in Scotts Bay in Wallagoot Lake by a I&I NSW Fisheries Officer on 31 July 2007. The lake is fished by both recreational and commercial fishers, who may also use their gear in adjoining estuaries on the south coast, which increases the risk of further spread to unaffected estuaries. Since November 2007 the Lake has also been the site of a I&I NSW prawn stocking project (in collaboration with University of NSW and Recreational Fishing Trust support) which has significantly increased numbers of recreational prawn fishers in the area.

The departments response after discovering Caulerpa in Wallagoot Lake has been to:

• comprehensively survey the lake each year to establish the size of the Caulerpa infestation;
• institute and revise recreational and commercial netting closures as appropriate; and
• conduct targeted control work in Caulerpa affected areas using both salt and manual removal by commercially certified departmental divers.

The control work to date has kept the Caulerpa infestation in check and further monitoring will be conducted during the summer 2009/10 to inform future management of Caulerpa at Wallagoot Lake.

In April 2008, a working group, called the Wallagoot Caulerpa Response Group, was established to provide advice and assistance in the fight against this noxious pest in Wallagoot Lake. The department has worked closely with this working group, and representatives from Bournda Environmental Education Centre, Bega Valley Shire Council, Southern Rivers Catchment Management Authority, Department of Environment and Climate Change, to ensure a whole of government approach that is well supported and assisted by the local community.

• Wallagoot Lake case study more information - updated November 2009
• Bournda Environmental Education Centre - Caulerpa taxifolia in Wallagoot Lake (www.bournda-e.schools.nsw.edu.au)

How can you help?

Check you do not have Caulerpa in your aquarium. If you do, dispose of it immediately by placing it in a plastic bag in your freezer for at least 24 hours, and then placing it in the garbage. NEVER release Caulerpa into a stormwater drain, creek, bay, lagoon, or the ocean.

If you have visited an infested estuary, inspect your anchor and chain, all fishing and diving gear, wetsuits, boat trailer, outboard motor and vessel. If you find any fragments of Caulerpa dispose of them in a bin to prevent contamination of other waterways.

If you think you have found Caulerpa in a new area, take a photograph or retain a sample and contact your local NSW DPI office or the Aquatic Biosecurity Unit (see below). Often new detections are a result of increased public awareness through NSW DPI education programs.

Avoid boating or anchoring in areas near Caulerpa outbreaks.