A remotely operated submersible built to remove invasive caulerpa seaweed began its final testing phase at Omākiwi Cove on 22 June 2026, following four years of development work.
The $5 million vehicle functions as a robotic underwater mower paired with a vacuum, moving across the seabed on rotating steel cylinders while extracting caulerpa plants and surface sediment. Designer Andrew Johnson of Johnson Bros said the 16-tonne vehicle is unique globally.
The machine can clear approximately 10,000 square metres each day, compared with early mechanical trials that achieved 2,500 square metres and initial diver-led efforts that removed roughly 70 square metres. "And we're aiming for a really high, 100% complete removal in a single treatment," Johnson said.
Operators manage the tethered robot from a control room aboard a surface barge, monitoring camera feeds, sonar and GPS data as the vehicle travels at 8 metres per minute. A 650-metre umbilical cable supplies power and control signals.
The vehicle uses hydraulic equipment sourced from a Scottish North Sea oil and gas vehicle originally built for depths up to 350 metres, along with parts from New Zealand, Australia and Germany. Constructed in Ōpua over 18 months, the 13-metre submersible was transported to Omākiwi Cove on 18 June.
Regional council biosecurity manager marine Kaeden Leonard said the machine's ability to extract large quantities of caulerpa from dense meadow areas was a potential game changer. "This takes us from manual harvesting to large-scale mechanical removal," Leonard said.
Invasive caulerpa was first detected on mainland New Zealand at Omākiwi Cove in May 2023. The seaweed had previously covered the equivalent of 115 rugby fields in the Bay of Islands, creating thickets up to half a metre high before beginning to die back in 2025 after sediment from Cyclone Tam smothered large areas. The caulerpa is now regrowing.
Johnson Bros built the submersible under a regional council project funded by Biosecurity New Zealand. The vehicle performed well during its initial four hours of testing on 20 June, with environmental monitoring results continuing to be assessed as trials progress.