Hauraki Plains College students visit seaweed growing trial that’s helping to heal Waihou River

Hauraki Plains College students learned about seaweed as it relates to farming.

Hauraki Plains College future scientists gathered in Kopu recently to grow their understanding of how and why to consider farming and learning about seaweed.

The Year 11 students were visiting the AgriSea bioremediation site in Kopu, where the seaweed species ulva has been grown in tanks on land to test its ability to draw unwanted nutrients from Waihou River water.

“This project gives seaweed a circular economy focus,” said AgriSea research technician Taylor Moore, who’s working on the seaweed-growing trial.

“As it grows naturally, you are using the seaweed to help remove some of the nutrients in the river water and then develop the seaweed afterwards into a product that reduces the need for the nutrients in the first place.

“If you want to farm seaweed, I could come to you with all the information you need and then I could buy it off you,” he said.

Taylor said the seaweed is put through processes at AgriSea to create biostimulants for farmers and growers. AgriSea also worked with Crown research institute Scion to innovate ways to create a type of hydrogel from the leftovers of their products, which can also be sold.

“You are getting multiple uses out of the seaweed and creating a value chain for it.”

The trial is a year long and there have already been discussions with councils about interest to expand it. The ponds are small and take up very little space, drawing water from the Waihou River before returning it after the seaweed has done its job in the tanks where seaweed grows.

“It’s not making a big impact but a system like this has the potential to create a massive impact for reducing nutrients in our waterways and cleaning up our rivers,” said Taylor.

Students asked questions about why the seaweed is moving in the tanks. In the ulva trial, a paddle wheel keeps the water mimicking the action of waves – which the seaweed needs to remain healthy.

Taylor said it was the most resilient plant he’d known.

“When I first came here I thought, ‘There’s no way this seaweed can grow in this half-salty water with the amount of mud and pollutants in this river, there’s no way’. We’ve had times that power has shut down and you can almost see that it’s struggling, but give it a day or two after you turn everything back on, it bounces back.”

He said while this project has been ongoing since March 2022, there’s insufficient data as yet to draw any meaningful trends.

“We had challenges including Covid contributing to shipping delays, but now that we’re in full swing, we’re learning constantly and it’s exciting to see the growth rates of the ulva species and how it copes with unpredictable events such as recent extreme weather.

”There are promising results with an average over a seven-week period of seaweed tripling its weight every week.”

Teacher Bronwin Dyer asked about a seaweed growing project where it is grown on ropes.

Taylor said this is another project to establish a different species – Ecklonia radiata - under the Greenwave system that was established up the coast off Coromandel Town to help kickstart the seaweed growing industry on the Coromandel Peninsula.