New Growth at Wilson’s Bay: Lessons in seaweed farming

When Greenwave Aotearoa first set out to grow native seaweed in the Hauraki Gulf, Wilson’s Bay off the Coromandel coast turned out to be a tough site. For months, the pilot struggled with fouling, heatwaves, and consent restrictions. But now, thanks to fresh thinking, local knowledge and hard-earned lessons, the story is changing. 

Ryan Marchington, Greenwave Aotearoa’s aquaculture operations lead, believes what’s behind the breakthrough is the collaboration around farm design changes. 

 “The whole thinking around our seaweed farm design has changed,” Ryan explains. “I’m not the expert in how to put the gear in the water, but I’d seen what worked overseas. So our partner seaweed farmer Dave Blyth [from Premium Seas] and I sat down and figured it out together. He’s spent his whole life as a mussel farmer. We realised that mussel-style farming doesn’t work for seaweed and we adapted.” 

 Seaweed farming is new in New Zealand, and the Greenwave Aotearoa team has been using systems that were designed for growing mussels rather than custom made for seaweed.  Dave has been contributing his 35+ years’ of experience in aquaculture to help the team optimise on-water operations, however there was still plenty to figure out about growing seaweed on systems primarily designed for mussel farming.

“It’s been a big learning process – and while you can grow seaweed in a hatchery, it doesn’t automatically follow that they’ll keep growing in the water,” shares Dave.

“I’ve enjoyed the process - especially the innovating. I love designing the gear and coming up with new ways of doing things and working with the young people from Greenwave Aotearoa and the University of Waikato. Peter [Randrup] and Ryan and all the guys are good, no-one has got all the answers. I never curtail their enthusiasm but it’s good to inject how to do things out on the water in a way that will make it easier and more efficient.” 

That collaboration between a seasoned mussel farmer and international seaweed farming techniques was a crucial turning point that seems to be paying off. Growing seaweed closer to the surface, as farmers do in Scotland, allowed the young sporophytes to photosynthesise more efficiently and outcompete fouling in their earliest stages. 

“Our hatcheries were producing good-quality spools. The issue was the design,” explains Ryan. “Once we changed that, we saw the difference.” 

Co-Locating for the Future 

Shifting our farm design meant navigating the regulatory process of consents and learning how to farm between existing mussel backbones. It’s not the most elegant setup, but it’s a necessary step in making use of the infrastructure that’s already in place. 

“This isn’t the end goal,” Ryan explains, “but it’s a big step forward. Think of it like growing different vegetables in the same field. We’re diversifying within the same growing space. That’s the future of co-location—farming seaweed alongside mussels, using the consented areas and infrastructure that are already part of our coastal environment.” 

Learning Through Challenges 

Given the challenges, it would have been easy after funding of the pilot ended to walk away from the site and move to another area where fouling pressure was less intense. Marine heatwaves, pests grazing on young seedlings, and biofouling tested the team’s persistence, while Covid-driven supply chain delays set the project back from the start. 

Still, each challenge produced new insights. University of Waikato scientists, Dr Marie Magnusson and Dr Rebecca Lawton, brought critical oversight to the trial, and project manager Rebecca Barclay-Cameron ensured expertise was brought in at every stage, including an guidance and advice from GreenWave, a non-profit organisation based in the United States that helps coastal communities establish regenerative ocean farms. 

When the seaweed Ecklonia radiata was failing, Peter Randrup shared at the time: “Ocean farming is like land farming and some sites just don’t suit certain crops.” 

But in recent months, the Ecklonia has been been growing well. "It’s looking particularly good. No fouling like we used to see back at Esk Pt, the ends aren’t tattered – it’s the most encouraged we’ve ever been. A really good sign," says Lucas Evans, CEO of Coromandel-based seaweed producer  Premium Seas. 

Greenwave Aotearoa founder Dr Nigel Bradly was present at the initial outplanting of the first seedlings in Wilson’s Bay and views the progress at Wilson’s Bay in the context of more than just one site’s success. 

“Unlike land-based farming, seaweed aquaculture in New Zealand doesn’t have decades of science and trial behind it,” he says. “What was historic here was cultivating not just one but two native seaweed species in a commercial hatchery and transferring them to farm settings. This is a new era for sustainable marine farming in New Zealand with potential benefits for biodiversity, ocean health, and coastal communities.” 

With the successful growth at Wilson’s Bay, the team anticipates possible future challenges to come. Says Dave: “As the seaweed achieves these good growth rates it’ll get heavier on the lines, and it may be a lot harder for it to hold on the rope with the [seaweed] holdfast. As it gets bigger we’ll need more floats, and that area has a fast flowing current since it’s at the bottom end of the block, which means they seawed gets the first bite at the food [nutrients]. 

“So going from 1kg per metre to 5 or 6 kg per metre will be interesting to see what happens.” 

But it’s a good fresh challenge to face. The journey at Wilson’s Bay shows what can happen when global ideas meet local expertise, and when perseverance outweighs early setbacks. Seaweed farming in Aotearoa is still young, but every new line in the water is helping shape a more resilient and regenerative blue economy.