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New Zealand’s kelp forests have been decimated by flooding debris

University of Canterbury Marine Science Distinguished Professor David Schiel underwater.

University of Canterbury Marine Science Distinguished Professor David Schiel underwater.
Photo: Supplied / University of Canterbury

New Zealand’s vital underwater kelp forests are being decimated by flood debris swept into the ocean after heavy storms.

University of Canterbury marine science professor David Schiel, co-leader of a five-year, $11 million research project investigating the problem, says it is a major concern for marine biodiversity.

Silt and other pollutants washing into the sea from flooded land were smothering habitats, Schiel said.

University of Canterbury Marine Science Distinguished Professor David Schiel

University of Canterbury Marine Science Distinguished Professor David Schiel
Photo: Supplied / University of Canterbury

“A large number of fish recruit as small fry in the kelp, they have a very lush undergrowth of other species, so in every square meter you are likely to encounter about 25 species.

“So when you get a rain of very fine sediment coming out of a watershed, this kind of clay flows over it like goo and it blocks the plants so they can’t even photosynthesize and grow,” he said. .

“What we’re seeing now in so many areas along the coast is that the bottom is covered in this thick, muddy stuff that has pretty much killed everything in the coastal area.”

Seaweed ecosystems such as kelp forests are important habitats for species such as pāua, cinchona, crayfish and fish species such as moki, blue cod and snapper.

Schiel said the research project – Toka Ākau Toitū Kaitiakitanga: Building a sustainable future for coastal reef ecosystems – was a collaboration between the University of Canterbury, the University of Otago, the University of Waikato, NIWA, Ngāti Pūkenga, along with other iwi and regional and district organizations. councils.

It was funded by the Ministry of Business, Innovation and Employment.

“We have some of the best researchers in the country looking at different aspects of the impacts, the sources of the sediment, tracking it through satellite and drone technologies and using remotely operated underwater vehicles,” Schiel said.

“We work in various catchments across the country, including the Bay of Plenty, Taranaki, parts of Southland and around the Marlborough Sounds and Kaikōura.”

Schiel, who also studied the impact of the 2016 Kaikōura earthquake on the marine environment, said storm-related runoff was a problem for most, if not all, of New Zealand’s coastline.

Exotic forestry was one of the big culprits, he said.

“We saw the effects of Cyclone Gabrielle in early 2023, when hail from recently harvested forestry blocks, along with torrents of water, mud and debris, crashed into the ocean, often burying kelp forests and their native species,” he said .

“We now need to find ways to improve coastal management and prevent runoff from land-damaging kelp forests. These are wide-ranging issues, but they go back to: how do we stabilize the soil and keep these pollutants on land and not allow them to grow, how can we harvest trees without damaging the marine environment?”

The Toka Ākau Toitū Kaitiakitanga project started a year ago and will run until 2028.