Exotic caulerpa seaweed unlikely to threaten Top of the South
01 November 2024
Exotic caulerpa is now known to be in nine locations – predominantly around the Hauraki Gulf but also in the Bay of Islands in Northland.
It is not, however, regarded as a significant threat to the upper South Island. The international science advice is that exotic caulerpa needs average winter water temperatures of approximately 15°C to survive and thrive. Scientists predict that the most liveable range for exotic caulerpa lies between Cape Reinga and East Cape on the north-eastern coastline of the North Island.
Since its discovery at Aotea Great Barrier Island, some $20 million has been spent or allocated on work to understand the pest (its distribution and biology), ways to survey for it and potentially remove or treat it, and work to prevent its spread.
While full eradication of exotic caulerpa at the scale present in New Zealand is not feasible, many tools and removal methods have been trialled, including salt application, benthic mats, UVC light treatment, diver-assisted suction dredging, mechanical suction dredging, hand removal, chlorine treatment, and using kina as a biocontrol.
Work continues to further develop some of these tools so they are more cost-effective, faster and effective at removing large areas of exotic caulerpa.
While exotic caulerpa is unlikely to appear in TOS waters, it is important that the area’s marine users follow some simple rules if visiting upper North Island areas – for example, for recreational boating and aquaculture activities.
- Avoid inadvertently spreading exotic caulerpa by ensuring that before you move locations, your anchor, anchor chain and marine equipment (fishing gear, nets etc) are free of entangled seaweed.
- If you find it, remove it, bag it and dispose of to the rubbish on land.
- Importantly, there are legal controls on anchoring and some fishing activities in place at some affected locations.
Photo credit ‘NIWA’