Two caulerpa removal projects now in the water
Two of the three significant projects to fast-track caulerpa removal tools are currently under trial in Omakiwi Cove in the Bay of Islands and will shortly move to the Hauraki Gulf.
'Rehabitat' chlorine treatment enclosure
This tool is a way of applying a mix of chlorine and freshwater to areas of exotic caulerpa in a controlled way that confines the chlorine to the specific area being treated.
An early prototype of the technology, which the developers are calling the 'Rehabitat', uses a metal frame with ‘curtains’ to contain the chlorine mix. This has been tested in recent weeks in Omakiwi Cove and is working very well.
The team is now refining the method with a move to an enclosure with inflatable sides. This can be filled with seawater to drop the Rehabitat over the treatment area, and then inflated with air to raise and move it.
The developers, Commercial Dive Specialists, say this method will be scalable and be able to be used over large areas and a variety of seabed surfaces. Next stages in the tool development will include trialling a continuous 24 hour per day operation.
Early results from the trials have shown the chlorine treatment to be very successful and able to kill caulerpa in a very short time minimising damage to other marine life in the area. The team has been able to determine the optimal dose and exposure time, and the method has been effective even against dense caulerpa.
UV-C light treatment
The UV-C light treatment trial is progressing well with the team completing three rounds of irradiating patches of exotic caulerpa in Omakiwi Cove, Northland.
The focus of this project is translating success in a laboratory to a field-scale model and the work has involved tuning the lighting frame to the environmental conditions at Omakiwi. This has meant adjusting the height of the lights over the plants and shifting from a continuously moving light frame to holding a position during treatment before moving on to the next patch.
The Advanced Aquarium Technologies team is testing use of the light technology on three different types of exotic caulerpa infestation – intertidal, thicker dense beds, and areas that have already been treated by suction dredge.
After assessing the treated areas, removal results are looking promising.
Northland submersible dredge planer
The third project is the development of a large-scale suction dredging tool to operate remotely on the seabed and remove large areas of caulerpa.
The Northland-based developers are building a submersible dredge head and working closely with engineers in Scotland who are creating a remote-operated vehicle that the equipment will be docked with. Trials in the water are scheduled for later in the year.
Beach cast clean-up after Cyclone Tam
Cyclone Tam that recently hit the upper North Island washed up many tonnes of exotic caulerpa on the beaches of Omakiwi Cove in Northland.
A volunteer army from iwi and the community gathered in the aftermath of the storm to move the beach-cast caulerpa above the high-tide mark to prevent it washing back into the water.
More than 200 people were involved in the mahi over the Easter weekend, and subsequently.
Biosecurity New Zealand has acknowledged the community effort and contributed to the costs of the clean-up with a $20,000 grant afterwards to Whangaroa Taiao Ltd who were key co-ordinators of the project, in collaboration with hau kainga. The grant will also help the community prepare for biosecure caulerpa removal in future weather events, funding the purchase of nets, collection bins, rakes and bleach stations to scrub down equipment.
Latest exotic caulerpa detections
Since we last updated on caulerpa locations, there have been a number of new detections in the Bay of Islands outside of the current controlled area in Omakiwi Cove. The new locations (see map below) are:
The channels between Motukiekie Island and Waewaetorea and Moturua Islands
Poroporo Island
Mohenoititi Islands (including Hauai)
Paradise Bay
Otaio Bay
Cable Bay
Waewaetorea Channel
Sunset Bay
Paroa Bay
Tapeka Point
This is a reminder that it is very important boaties, fishers and divers take care to avoid accidentally spreading exotic caulerpa.
First, follow the rules of the Controlled Area at Omakiwi Bay (see map below). These legal requirements make it illegal to anchor in this area unless it’s an emergency or you have a permit from Biosecurity New Zealand. All forms of fishing are prohibited in the Controlled Area, and you cannot dive there.
Outside of the CAN, in all other Northland waters, before you move to a new location, check your vessel’s anchor and anchor chain, as well as any other gear that has been in the water such as a fishing line or dive equipment.
If you find any seaweed attached – remove it, bag or contain it securely and take it ashore for disposal.
On shore, dispose of the seaweed in rubbish bins away from the ocean or in the household rubbish.
For more information click here