Caulerpa taxifolia

Photo: Alan Millar, Royal Botanic Gardens, Sydney

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.

Photo: David Harasti

Caulerpa filiformis

Key features:

Flattened strap-like fronds (not fern-like)

Habitat:

Exposed and sheltered rocky reef and sandy areas, to 6m depth
Common between Port Stephens and Jervis Bay

Photo: John Huisman, Marine Plants of Australia

Caulerpa scalpelliformis

Key features:

Fern-like fronds with leaflets either side of fronds not directly opposite each other

Habitat:

Exposed rocky reef to 36m depth

Photo: John Huisman, Marine Plants of Australia

Caulerpa flexilis

Key features:

Fern-like branchlets with secondary leaflets

Habitat:

Exposed rocky reef to 40m depth
More common in deeper water

Photo: John Huisman, Marine Plants of Australia

Caulerpa cactoides

Key features:

Short rounded club-like leaflets

Habitat:

Sheltered and less exposed sand, mud and rock surfaces up to 38m depth

Natural distribution & biology

Dense Caulerpa growing in Wallagoot Lake in May 2009 (Photo: James Sakker NSW DPI)

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, and has been detected in 14 estuaries and one oceanic population (near Cronulla) in NSW. NSW DPI conducts regular surveys in known Caulerpa locations and periodically surveys adjacent estuaries, to assess changes in the distribution of the species.

Surveys conducted by NSW DPI researchers in late 2011/early 2012 found that the abundance of Caulerpa had declined significantly in all south coast estuaries (St Georges Basin, Lake Conjola, Narrawallee Inlet, Burrill Lake, Durras Lake and Batemans Bay to the point that little if any could be found. In contrast, Caulerpa abundance in most Sydney estuaries has remained more stable over recent years. The recent decline in Caulerpa (and native seagrass) in south coast estuaries may be a result of enormous fluctuations in salinity (due to a drought followed by major rainfall events in 2011 and 2012).

Caulerpa abundance is known to "boom and bust", and NSW DPI will continue to monitor estuaries where Caulerpa is known. It is quite possible that small Caulerpa beds may remain in many south coast estuaries. NSW DPI has a process for revocation of Caulerpa Closures which requires three consecutive years of comprehensive survey data that did not detect Caulerpa. The current Section 8 Caulerpa closure for the south coast estuaries will remain in place until sufficient data is available to support its revocation.

The DPI Aquatic Biosecurity team encourages waterway users to be vigilant to help minimise the spread of this noxious marine alga by avoiding affected areas and by inspecting all fishing and boating gear and removing and disposing of fragments by placing them in a plastic bag and into general waste. After removing all visible fragments, Aquatic Biosecurity recommends washing anchors, chains and other gear using freshwater before moving to another estuary.

Lake Macquarie, where Caulerpa was first detected in 2001, is now considered Caulerpa free. No Caulerpa has been found since 2006 and based on three consecutive years of comprehensive survey data the Section 8 Fishing Closure (Caulerpa) was revoked in Lake Macquarie in 2009. A map of previous distribution of Caulerpa in Lake Macquarie is available here:

Lake Macquarie (Map based on survey data since 2001; however, considered Caulerpa free since 2009) 3.2Mb

Cumulative distribution maps (showing all known locations) of Caulerpa have been prepared from NSW DPI Aquatic Ecosystems survey data, and are available by accessing the links below.

Important note: The following maps are indicative only and may contain errors and omissions. Maps are based on surveys of selected areas within the waterways not on exhaustive searches. Caulerpa may occur in additional areas not shown on the maps. Furthermore, the distribution of Caulerpa can change markedly over time, either expanding or contracting (for example, it can die back during winter and grow 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 these maps 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:

How did it get here?

Fragments of Caulerpa can be spread by anchor chains (Photo: Melissa Walker, NSW DPI)

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 native seagrasses are not impacted by Caulerpa, although some questions still remain about possible effects on sparse beds of Zostera capricorni.

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 over the last five years that DPI research staff conducted surveillance to monitor changes in those populations.

Estuary	2008	2009	2010	2011	2012
Lake Macquarie	Apr	-	Jan	-	-
Brisbane Water	-	-	Apr	Mar	-
Pittwater	Mar, Nov	May	-	-	Feb
Port Jackson	Jan	-	-	Mar	-
Botany Bay	Jan	-	-	Feb	-
Port Hacking	Mar, Oct	-	-	Feb	-
St Georges Basin	Feb, Nov	Apr	-	-	-
Lake Conjola	Mar, Nov	Feb	-	Apr	May
Narrawallee Inlet	Mar	Feb	-	-	-
Burrill Lake	Mar, Oct	Feb	-	Apr	Mar
Durras Lake	-	Feb	-	-	-
Batemans Bay	-	Feb	-	-	-
Wallagoot Lake	-	Feb, May, Jun	Nov	-	Feb

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

Table 1. Details of past five 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.

Successful eradication of Caulerpa taxifolia in Wallagoot Lake - Case Study - updated June 2013

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 Merri Reef. It has also been discovered in waterways in South Australia.

The most recent discovery of Caulerpa was confirmed in Scotts Bay, Wallagoot Lake, by a NSW DPI Fisheries Officer 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. From 2007-2009 the Lake was the site of a NSW DPI prawn stocking project (in collaboration with University of NSW and Recreational Fishing Trust) which significantly 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
Conduct targeted control work in Caulerpa affected areas using both salt and manual removal by commercially certified departmental divers.

In April 2008, 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, the former Southern Rivers Catchment Management Authority (now Local Land Services), Department of Environment Climate Change and Water(now Office of Environment and Heritage). This holistic agency approach was well supported and assisted by the local community.

Comprehensive surveys conducted by the Caulerpa Response Group during late 2010, 2011 and early 2013 failed to detect Caulerpa in Wallagoot Lake. Three consecutive years of monitoring without detection meets the DPI threshold for successful eradication of an introduced species from a water body. As such, the Section 8 Fishing Closure that was placed over Scotts Bay upon discovery of Caulerpa in 2007 was formally revoked on Friday 3 May 2013.

Caulerpa taxifolia in Wallagoot Lake - Case Study - updated June 2013

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.