A 16 tonne underwater machine that looks like nothing else on the planet has begun clearing one of New Zealand’s worst marine pests from the seafloor of the Bay of Islands, and the engineers behind it believe it can do in a day what divers once took weeks to manage.
The $5 million remote underwater vehicle was launched at Omākiwi Cove on 22 June and completed its first full four hour operation the following day. It is designed and built by Ōpua marine contractor Johnson Bros, and according to RNZ it is the only machine of its kind anywhere in the world.
Its target is exotic caulerpa, a fast spreading green seaweed that smothers the seabed in dense meadows and crowds out native marine life. The weed was first confirmed on the New Zealand mainland at Omākiwi Cove in May 2023, and it has since carpeted the equivalent of about 115 rugby fields across the Bay of Islands. Around Great Barrier Island the spread has been far worse, covering more than 1,100 rugby fields of seafloor.
Until now the response has relied on divers manually guiding suction dredges, painstaking work that cleared only around 70 square metres of seabed a day. Earlier mechanical trials lifted that to roughly 2,500 square metres. The new machine is built to remove about 10,000 square metres a day, the equivalent of around one and a half rugby fields, and to do it in a single pass.
The vehicle is 13 metres long and 2.5 metres high, with a footprint of about 52 square metres. It crawls across the seabed at roughly 8 metres a minute, driven not by wheels or tracks but by two seven metre Archimedes screws, steel cylinders wrapped in corkscrew blades that turn to push it forward over soft sediment. A planing head at the front works on the same principle as a wood planer, shaving off the caulerpa plant along with its stolons and rhizomes, the runners and roots that let it regrow, plus about 7 centimetres of surface sediment underneath.
That material is vacuumed up to a barge on the surface, where sand and water are separated out and returned to the sea. Operators run the whole thing remotely from a control room on the barge, connected to the machine by a 650 metre umbilical cable.
Designer Andrew Johnson, who holds an ocean engineering degree from the University of Tasmania, told the New Zealand Herald the build was a genuinely Kiwi solution to a problem that is already reshaping coastal life. “There is nothing like this anywhere else in the world,” he said. “It’s a technically ambitious, innovative solution to a really big problem facing New Zealand that’s already significantly changing the Kiwi way of life.”
Johnson said the cost would have been far higher overseas. “If this had been built anywhere else in the world, it would have cost hundreds of millions of dollars,” he said. The machine took 18 months to build in Ōpua and caps off about four years of work since caulerpa first turned up on the mainland.
The project sits under Northland Regional Council and is funded by Biosecurity New Zealand, a unit of the Ministry for Primary Industries. The launch at Omākiwi was attended by members of the local hapū, the sub-tribes who hold the area, along with council and ministry officials.
Northland Regional Council marine biosecurity manager Dr Kaeden Leonard said the machine marked a step change in how the country could respond. “This takes us from manual harvesting to large-scale mechanical removal,” he said. Derek Richards, the council’s marine biosecurity specialist and project lead, was more cautious about what lies ahead. “We never really know what’s going to happen next with new invasive pests,” he said.
That uncertainty is real. Caulerpa at Omākiwi had grown into meadows up to half a metre high before a major dieback began in 2025, when sediment stirred up by Cyclone Tam smothered large patches of the weed. But the seaweed has since started regrowing, a reminder that natural setbacks do not amount to a cure.
The weed spreads easily on anchors, fishing gear and bilge water, which is why controlled anchoring rules and equipment checks have been in force across affected parts of Northland and the Hauraki Gulf. If the new machine performs as hoped through its trials, it offers something the response has lacked so far, a way to clear infestations at a scale that might actually keep pace with how fast caulerpa moves.
What do you make of New Zealand building its own world first answer to caulerpa? Have your say in the comments below.
This article was written by AI, briefed to report the facts, hopefully without some of the bias people bring to the job 🙂
Leave a Reply