Ryan Marchington is the aquaculture and science operations lead at Greenwave Aotearoa. Ryan oversees all seaweed farming operations, including on-water farming, harvesting, and the initial stages of processing.
Thousands of baby seaweeds on twine are spooled onto ropes at sea – their holdfasts anchor, and the plants grow from there." - Ryan Marchington.
"Seaweed farming isn’t one-size-fits-all. You’ve got to tweak what’s known to suit local species and conditions."
"We’re co-farming mussels, scallops, and seaweed on the same lines – using what already exists more efficiently."
Q: Where were you heading on the day of this interview?
We were in the Hauraki Gulf, heading down into the Firth of Thames to Wilsons Bay – a major aquaculture block. We’re working on establishing the first dedicated seaweed farms in this area, which is a significant step forward for New Zealand.
Q: Where else is seaweed being farmed?
Currently, we’re farming in two locations – up here in the Hauraki Gulf and down south in the Marlborough Sounds, specifically Tory Channel. We’re also exploring expansion further south, toward the bottom of the South Island.
Q: What are the main differences between the sites?
The differences are striking. In the Hauraki Gulf, the water is warmer and more silty. In the Marlborough Sounds, the water is colder, and the fouling communities are different. We’re also working with different seaweed species at each site, tailored to local conditions.
Q: How does your background influence your work here?
I’m originally from the UK, where I ran a commercial hatchery. Over there, seaweed farming is supported by dedicated infrastructure like processors and hatcheries. In New Zealand, we’re still in the early stages of developing these capabilities, which is exciting but also challenging.
Q: Is it easy to apply international seaweed farming knowledge in New Zealand?
Seaweed species differ across regions, as do environmental conditions like temperature, sedimentation, and available infrastructure. While some techniques are transferrable, most need to be adapted to suit local conditions.
Q: What’s unique or exciting about New Zealand seaweed?
New Zealand’s kelp species, like Macrocystis (giant kelp), are amazing. They form huge underwater forests that float in the water. Coming from the North Atlantic where kelp is smaller and less buoyant, it’s fascinating to work with these canopy-forming species.
Q: What keeps you passionate about seaweed?
Seaweed is a huge part of our coastal ecosystems. It’s exciting to work on farming something that has so much potential – both environmentally and economically. I talk about it at work and outside of work – probably too much! But it really does consume your life in a good way.
Q: Did you grow up by the ocean?
No – I’m from Manchester and didn’t grow up near the sea. My love for the ocean came from holidays in Wales, fishing and exploring beaches near my grandparents’ place. I studied marine biology in Newcastle, then specialised in algae and ran a hatchery in Scotland before moving here.
Q: Tell us about the Greenwave work happening in the Firth of Thames.
We’re installing New Zealand’s first dedicated long-line seaweed farming structures. We’re using catenary systems – curved long-lines between mussel farm backbones. It’s a co-farming model where mussels, scallops, and seaweed grow together, using existing aquaculture space more efficiently.
Q: What challenges do you face in growing seaweed here?
The biggest challenge is space. We’re relying on existing aquaculture areas, which aren’t always ideal for seaweed. Mussel farms are usually in sheltered waters, but seaweed prefers areas with more current and exposure. Also, existing consented structures – mussel backbones with droppers – aren’t necessarily the best for seaweed. We need updated consents to trial horizontal submerged lines.
Q: How have government and councils responded to this innovation?
They’ve been very receptive. It’s encouraging to see regulators working with us to trial and approve the new systems needed to make seaweed farming viable.
Q: What about biological challenges like fouling or sediment?
Yes, those are significant. In some areas, sedimentation smothers the seeded lines, making it hard for young seaweed to establish. In others, like the Hauraki Gulf, we face heavy fouling pressure from hydroids and skeleton shrimp. In the Marlborough Sounds, we also contend with competing macroalgae. These challenges are why pilot studies are so critical.
Q: Can you explain the process of transferring seaweed from hatchery to farm?
Sure. From the hatchery, we transport spools laden with thousands of baby seaweeds – called sporophytes – in cool, moist containers. At the farm, we run grow ropes through the spools, which wraps the seaweed around the rope. The seaweed’s holdfast (like its root) grows into the rope, anchoring it as it matures. You’ll see this in action during our farm work today.
