Caulerpa Taxifolia

caulerpa Caulerpa Taxifolia (CT) is an invasive marine plant or seaweed threatening some coastal ecosystems in Australia by taking over from the native marine flora (such as seagrasses). It adversely alters the marine habitat of fish, crustaceans, molluscs, etc and causes a decrease in biodiversity. It is present in several NSW coastal lakes including 3 on the South Coast - Burrill, Narrawallee, and Conjola. It is bright green in colour, has a stem which can be over a metre in length and 5 to 60 cm long fronds.

The image is courtesy Alan Millar, Royal Botanic Gardens Sydney.

CT occurs naturally in tropical waters, including those of Australia. It is now believed that over thirty years ago specimens were sent from Queensland to Europe for use in aquariums. Over time a cold water tolerant, fast growing strain was developed. This strain is extremely invasive - for example, thousands of hectares of the Mediterranean have been infested. In NSW the plant has been declared a noxious species. While it may be kept in a properly enclosed aquarium, the sale of the plant is prohibited (large fines apply).

CT is very easily spread; small pieces can start a new plant. It is also very robust, being able to survive a week out of water provided it is kept in a warm damp spot. Furthermore it is very difficult, perhaps impossible, to eradicate once it is well established. Many attempts have been made to get rid of this weed, methods ranging from hand picking to covering it with kilograms of salt. The use of swimming pool salt seems promising, and is being investigated by NSW Fisheries. In initial tests as much as 1 tonne of salt was laid over an area of 10 square metres and found effective in killing CT. Presently the Fisheries scientists are testing the effectiveness of lesser quantities. CT is sensitive to the salt content of its aquatic environment; it cannot tolerate too little (i.e. fresh water) or too much. While the salt may dissolve in a couple of hours, a high-salt-content layer of water remains and the CT dies within a couple of days. It seems that the invasion in Narrawallee is under control thanks to the use of salt but the invasion in Lake Conjola is much more significant (an area of 156 hectares is affected) and it may not be feasible to remove this.

Unfortunately there is now a small (6.5 hectares) infestation in Saint Georges Basin - close to Basin View. NSW Fisheries are attempting to eradicate this with salt. It is important not to spread this weed further; it could be a disaster if it became established in the Basin. There is a need to be vigilant. After boating, fishing, or diving in contaminated waters boats and gear should be inspected. Wash down areas are now provided at boat ramps. Any pieces of CT collected should be bagged prior to disposal. The areas beside boat ramps are the very spots where one would expect CT to first take hold and are the first areas which should be inspected.

Further Information

Royal Botanic Gardens Sydney ( www.rbgsyd.nsw.gov.au)
NSW Fisheries (www.fisheries.nsw.gov.au)


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