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Biosecurity New Zealand widens search for invasive sea squirt


Bull Kelp- From filaments to fish food for a habitat-forming alga

Study in our coastal waters, examining growth and survival of different life-stages across gradients of wave exposure.  By David Taylor, University of Canterbury, New Zealand

Beware this seaweed !!

Caulerpa taxifolia is native to the tropical Atlantic, Pacific, and Indian Oceans, and its attractive growth form has made it popular with people who keep saltwater aquariums. It has become a major problem, however, because of a robust and cold-tolerant strain developed at Stuttgart Zoo under artificial aquarium conditions. This strain was then transferred to Monaco. It can grow up to 8 cm a day, tolerate complete darkness, and survive out of water for up to 10 days – and regrow from tiny fragments. It can grow at depths of between 3 and 35 m, though it has been recorded at 100 m.

The "normal" form of this tropical seaweed has specific growth requirements for warmer water, cannot tolerate exposure to air or long periods of dark, and has a much more restricted ecological range.

A small amount of C. taxifolia was recently found in a saltwater aquarium in Auckland, causing a great deal of concern. Was it the tropical or aquarium strain? Did it occur elsewhere in New Zealand? Was there a risk of fragments being released into the environment when aquarium owners cleaned their tanks?

Visit NIWA site to see the answers to these questions:



Biosecurity New Zealand widens search for invasive sea squirt

Biosecurity New Zealand’s extended surveillance for the sea squirt the clubbed tunicate begins this week, with divers searching Northland waters.

The sea squirt has to date been confirmed in parts of Auckland’s Hauraki Gulf and in Lyttelton Port.

Now Biosecurity New Zealand needs to know if there are other infected locations around New Zealand to help plan any future action.

Senior Marine Advisor Brendan Gould says surveying so far indicates the organism has been in the country for some years and may have spread to areas outside the Hauraki Gulf and Lyttelton.

The National Institute for Water and Atmospheric Research (NIWA) has helped design the national surveillance programme and is undertaking the surveillance work for Biosecurity New Zealand.  It is focusing on sites considered to be at high risk of spread due to their proximity to known infestations, or that have a high volume of inward vessel movements. (See footnote for locations). 

Along with the surveillance, Biosecurity New Zealand is asking members of the public, especially marine users, to keep an eye out for the clubbed tunicate sea squirt and report any suspected finds to its free 0800 number (0800 80 99 66).

Awareness material about the sea squirt is being spread through media and a variety of media channels used by boaties, aquaculture industry and divers.

And Biosecurity New Zealand is also embarking on further studies looking at possible control and treatment options for the pest.

Research will look into a range of control measures which include wrapping infected structures with plastic, injecting acetic acid into the wrap and dipping in acetic acid for equipment.

While this wider picture of the sea squirt’s presence and treatment options is compiled, Biosecurity New Zealand is also asking for help from all marine users to prevent the spread of the creature.

“It’s really important that boaties come on board with the effort to curb its spread.  Marine users must now take responsibility for keeping their vessel hulls and equipment clean and free of fouling,” Mr Gould says. 

Biosecurity New Zealand says where people are preparing to move to another region, they should ensure the hull of their vessel is clean.  “We’re asking people to check their hull before setting sail and where it is heavily fouled, to clean it where it is,” Mr Gould says.

It is known that regular cleaning and the use of anti-fouling treatment will greatly help

contain the spread of the sea squirt.  The organism prefers a dirty boat to hang

onto and if hulls and equipment are clean, the sea squirt is unlikely to be transferred.

Preliminary start dates and locations for initial surveillance are:

Whangarei: Basin Marina, Marsden Point Port over next week (starting today)

Akaroa - Wednesday 2 November

Lyttleton – Thursday 3 November

Greymouth - Wednesday 9 November

There will be surveillance scheduled in the near future for the following areas identified as high-risk due to proximity to known infestations or vessel movements.

These are:

Bay of Islands (Opua)

Mangawhai Harbour


Nelson Port

Wellington Port



Dunedin Port

Napier Port

New Plymouth

Whakatane Port

Whitianga Marina

Tauranga Port

Photo opportunities can be arranged through Biosecurity New Zealand communications – see numbers below.  The teams working on the surveillance will not be free for interviews and any information about the work and the results will come from Biosecurity New Zealand.

Further information about the clubbed tunicate is also available on the Biosecurity New Zealand website: www.biosecurity.govt.nz/seasquirt

For further information, please contact:

Lesley Patston, Senior Communications Adviser, Ph. 027 205-1418

Or Phillip Barclay, Senior Communications Adviser, Ph. 027 229-9145


Bull Kelp- From filaments to fish food for a habitat-forming alga

David Taylor

Marine Ecology Research Group

School of Biological Sciences, University of Canterbury

Christchurch, New Zealand

Email: david.taylor@canterbury.ac.nz

Bull kelp, Durvillaea antarctica, forms a conspicuous margin along much of the exposed rocky coastline of the southern New Zealand, but also occurs across the southern hemisphere at latitudes between 45-60oS. Plants can reach up to 10m in length and weigh in excess of 100kg, and provide habitat for a myriad of invertebrate species in and around their holdfasts. In New Zealand, much of the ecological of D. antarctica has focused on the productivity of populations , and the processes determining its vertical distribution . My research has explored some of the processes determining its distribution along intertidal shores. In particular, I have examined factors affecting the growth and survival of different life-stages across gradients of wave exposure.

Despite growing in great abundance on exposed shores, and possessing mechanisms that enable it to attach at its earliest life stages , Durvillaea antarctica is rarely found in sheltered areas. To understand why this is, I transplanted the microscopic stages of D. antarctica across wave exposures at replicate sites on the east coast of the south island using a method pioneered by the Marine Ecology Research Group (MERG) at the University of Canterbury. This method allows us to transplant the microscopic stages (<100 microns in length) of several species of fucoid algae into varying environmental conditions and monitor growth and survival. My experiments found that at sheltered sites the growth and survival of the fine microscopic filaments of D. antarctica were greatly affected by the scouring and smothering effects of sediments. Consequently, after 64 days plants at exposed sites were more than twice the length (4-6mm) of plants at the more sheltered sites (2mm), and survival at sheltered sites was poor .

I also tested the effects of grazing by invertebrate molluscs, like limpets and chitons, on survival of Durvillaea antarctica across exposures. These experiments showed that, while their effects on survival across wave exposures can be great at times, the long term effects of sedimentation and scouring are more important in determining the distribution of the early life-stages. However, the reason for the often abrupt transition from D. antarctica to other species of brown algae in more sheltered areas was still not completely explained by these results.

When exploring possible reasons for this, I observed that recruits of Durvillaea antarctica outside adult canopies were often grazed back to the stipe by the common butterfish, Odax pullus. To further explore the importance of butterfish grazing, I transplanted recruit stages (10-15cm long) of D. antarctica across wave exposures at Banks and Kaikoura peninsulas. I found that within 30 days, plants at more sheltered sites were grazed back to their stipes by butterfish. Some plants at exposed sites were also grazed, but others escaped grazing and it appeared that survivors gained protection from remnants of adult canopies.

In order to understand the role of adult Durvillaea antarctica canopies in protecting recruits from fish grazing I transplanted recruits under and outside cages in different canopy treatments. I found that plants outside canopies were 3 times more likely to be grazed by butterfish than those under adult canopies. It seems that not only are the early life-stages of Durvillaea antarctica restricted by the effects of sediments in sheltered areas, but the soft, flat blades of the recruit stage are readily consumed by the herbivorous fish Odax pullus; particularly if they recruit away from the protection of adult Durvillaea canopies.

This example highlights the importance of experimental science in understanding the processes affecting the distribution and abundance of key habitat-forming species, and has important implications for the management and conservation of this significant marine system.

References available.