Introduction

Caulerpa taxifolia (Caulerpa) is a fast growing marine alga 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 alga 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 alga; 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.

Identification

Key features

• Frond height 3-25cm
• Flattened fronds, bright green colour
• Known to turn pale & white during winter in colder waters
• Leaflets on fronds attach directly opposite each other, curve upwards
• Leaflets constricted at base

Similar native species

These native species may be confused with this marine pest.

Natural distribution & biology

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 aquaria. 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 is a green marine 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 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.

Caulerpa reproduces sexually and asexually 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: The following maps are indicative only and may contain errors and omissions. The maps are based on surveys of areas where Caulerpa has been known to occur or has been reported, not on comprehensive surveys of the entire waterway.Caulerpa 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 the 24 hour hotline, 02 4916 3877 or email aquatic.pests@industry.nsw.gov.au.

This invasive seaweed has been identified in the following locations:

• Caulerpa taxifolia Closure - Narrawallee Inlet, Burrill Lake, Lake Conjola and Berringer Lake, Pittwater and St Georges Basin  244.1 KB
  
• Batemans Bay (Map based on survey data since 2007)  608.0 KB
  
• Botany Bay (Map based on survey data since 2001)  2.6 MB
  
• Brisbane Water (Map based on survey data since 2006)  2.3 MB
  
• Durras Lake (Map based on survey data since 2007)  430.5 KB
  
• Lake Macquarie (Map based on survey data since 2001; however, considered Caulerpa free since 2009)  3.2 MB
  
• Hawkesbury River - Patonga (Map based on survey data since 2007)  349.3 KB
  
• Port Hacking (Map based on survey data since 2000)  1.6 MB
  
• Port Jackson (Map based on survey data since 2002)  1.7 MB
  
• Wallagoot Lake (Map based on survey data since 2007)  343.7 KB
  

How did it get here?

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

After arriving in NSW, Caulerpa seems to have been spread from one estuary to another 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 marine alga on aquatic ecosystems. The impacts of Caulerpa infestations on local seagrass populations have been well researched (Ceccherelli and Cinelli 1997; Ceccherelli and Sechi 2002; Holmer et al. 2009). 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 can grow rapidly, leading to concerns it could out-compete native seagrass. Secondly, small fragments of Caulerpa can grow into new plants and create large colonies. Research results to date from NSW indicate that dense native seagrass beds are relatively resistant to invasion from Caulerpa, however, sparse seagrass beds (Zostera in particular) may be at risk from Caulerpa.

The numbers 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 by Gribben and Wright (2006) focusing on the impacts of Caulerpa on invertebrates living in and on sediments has found that the cockle Anadara trapezia recruits in greater numbers to Caulerpa than 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 and in the sediments under Caulerpa. Taylor et al. (2010) demonstrated that when Caulerpa gets washed onto the shore (“wrack”) and decomposes, the detritus it creates can adversely affect invertebrates living in intertidal sediments

What is DPI doing?

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

The program has included the removal of the alga 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.

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 alga 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 marine alga. 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 protected native seagrass, and so it is not possible to apply salt to Caulerpa which invades Posidonia beds.

DPI continues to survey a range of estuaries along the coastline, particularly areas north and south of infested estuaries such as Lake Conjola and Burrill Lake. These surveys resulted in the discovery of Caulerpa in both Batemans Bay in February 2007, and Durras Lake in April 2007.

DPI has established long term monitoring plots in several estuaries to assess the impact of Caulerpa on native seagrasses and we are also monitoring the rate of spread of known populations. Table 1 below shows, for each known location of Caulerpa, the dates DPI research staff conducted surveillance to monitor changes in those populations. This monitoring is implemented as part of the Monitoring Evaluation and Review (MER) program, and will continue into 2012.

Estuary	2007	2008	2009	2010	2011
Lake Macquarie	Aug	Apr	-	Jan	-
Brisbane Water	Aug	-	-	Apr	Mar
Pittwater	May	Mar, Nov	May	-	-
Port Jackson	-	Jan	-	-	Mar
Botany Bay	-	Jan	-	-	Feb
Port Hacking	May	Mar, Oct	-	-	Feb
St Georges Basin	Feb, Nov	Feb, Nov	Apr	-	-
Lake Conjola	-	Mar, Nov	Feb	-	Apr
Narrawallee Inlet	Mar	Mar	Feb	-	-
Burrill Lake	Feb	Mar, Oct	Feb	-	Apr
Durras Lake	Apr, Aug	-	Feb	-	-
Batemans Bay	Feb, Apr, Nov	-	Feb	-	-
Wallagoot Lake	Sep	-	Feb, May, Jun	Nov	-

- signifies no sampling undertaken in that year (or in 2011, none to date)

Table 1. Details of past three years of Caulerpa monitoring as part of the MER program in 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 was reviewed and updated in 2009 to reflect the latest research findings.

Caulerpa taxifolia in Wallagoot Lake - Case Study - updated November 2011

Executive Summary

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

The most recent discovery of Caulerpa was confirmed in Scotts Bay, Wallagoot Lake in 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. During 2007-2008 the Lake was the site of a NSW DPI prawn stocking project (in collaboration with University of NSW and Recreational Fishing Trust) which has increased numbers of recreational prawn fishers in the area.

The department’s response after discovering Caulerpa in Wallagoot Lake has been to:

• comprehensively survey the lake each year to monitor 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.

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, which includes representatives from the Bournda Environmental Education Centre (Bournda EEC), Bega Valley Shire Council, Southern Rivers Catchment Management Authority, Department of Environment Climate Change and Water, to ensure a whole of government approach that is well supported and assisted by the local community.

Monitoring has been undertaken by staff from the Bournda EEC on a regular basis and it appears as if control work to date has kept the Caulerpa infestation at low levels. NSW DPI is planning to survey the area comprehensively in late 2010 to inform future management of Caulerpa at Wallagoot Lake.

• Caulerpa taxifolia in Wallagoot Lake - Case Study - updated November 2011

How you can help

Check you do not have Caulerpa in your aquarium – it is illegal in NSW! 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 collect a sample and promptly contact your local NSW DPI fisheries office or the Aquatic Biosecurity team. Often new detections are a result of increased public awareness through NSW DPI education programs.

Avoid boating or anchoring in areas near Caulerpa outbreaks.

For more information on how to clean your boat to prevent the spread of marine pests you can download the booklet for recreational boaters (1.2 mb, ).

References and further reading

• Ceccherelli, G. and Cinelli, F. 1997. Short-term effects of nutrient enrichment of the sediment and interactions betweenm the seagrass Cymodocea nodosa and the introduced green alga Caulerpa taxifolia in a Mediterranean bay. J Exp Mar Biol Ecol 217:165-177.
• Ceccherelli, G. and Sechi, N. 2002. Nutrient availability in the sediment and the reciprocal effects between the native seagrass Cymodocea nodosa and the introduced rhizophytic alga Caulerpa taxifolia. Hydrobiologia 474:57-66.
• Gribben, P.E. and Wright, J.T. 2006. Sublethal effects on reproduction in native fauna: are females more vulnerable to biological invasion? Ocologia 149:352-361.
• Holmer, M., Maraba, N., Lamote, M. and Duarte, C.M. 2009. Deterioration of sediment quality in seagrass meadows (Posidonia oceanica) invaded by macroalgae (Caulerpa sp.). Estuaries Coasts 32:456-466.
• Noxious marine alga Caulerpa taxifolia in NSW (Primefact 1009)
• NSW Control Plan for the noxious marine alga Caulerpa taxifolia
• Taylor, S.l., Bishop, M.J., Kelaher, B.P. and Glasby, T.M. 2010. Impacts of detritus from the invasive alga Caulerpa taxifolia on a soft sediment community. Marine Ecology Progress Series 420:73-81.
• York, P.H., Booth, D.J., Glasby, T.M. and Pease, B.C. 2006. Fish assemblages in habitats dominated by Caulerpa taxifolia and native seagrasses in south-eastern Australia. Marine Ecology Progress Series 312:223-234.