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 flooding debris swept into the ocean after severe storms.
University of Canterbury Marine Science Distinguished Professor David Schiel - the co-leader of a five-year $11 million research project exploring the problem - says it is a major concern for marine biodiversity.
Silt and other contaminants washed into the sea from flooded land were smothering habitats, Schiel said.
University of Canterbury Marine Science Distinguished Professor David Schiel Photo: Supplied / University of Canterbury
"A vast array of fish recruit as little ones into the kelp, they have a very lush understory of other species so in any square metre you're probably going to get about 25 species.
"So, when you get this rain of really fine sediment that comes out of a catchment it pours down this sort of clay like claggy stuff on top of it and it blocks the plants so they can't even photosynthesise and grow," he said.
"What we see in so many areas around the coast now is that the bottom is covered with this thick mucky stuff that's virtually killed everything in the nearshore area."
Seaweed ecosystems like kelp forests are important habitats for species like pāua, kina, crayfish, and fish species like 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, University of Otago, University of Waikato, NIWA, Ngāti Pūkenga, along with other iwi and regional and district councils.
It was funded by the Ministry of Business, Innovation and Employment.
"We've got some of the top researchers in the country looking at different aspects of the impacts, the sources of the sediment, the tracking of them through satellite and drone technologies and using underwater remotely operated vehicles," Schiel said.
"We're working in different catchments around 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 run-off 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 early in 2023 when slash from recently harvested forestry blocks cascaded down slopes along with torrents of water, mud and debris and swept down into the ocean, often burying kelp forests and their resident species," he said.
"We now need to find ways to improve coastal management and prevent run-off from land damaging kelp forests. These are wide-ranging problems, but they go back to- how do we stabilise soils and keep these contaminants on the land and not allow them to dump into the sea? How can we harvest trees without damaging the marine environment?"
The Toka Ākau Toitū Kaitiakitanga project began a year ago and runs until 2028.
