Through Maia HartLocal Democracy Reporter
Four sections of cinchona have been removed in the Marlborough Sounds as part of a research project to rejuvenate seaweed and kelp on reefs.
It comes after widespread loss of kelp and other seaweed species in Tōtaranui/Queen Charlotte Sound has been linked to climate change, increased sedimentation and increases in cinchona.
Nick Shears, an associate professor of marine science at the University of Auckland, told Marlborough councilors during a presentation to the environmental committee that cinchona had been removed from four sites, including Ruakākā Bay, Blumine Island/Ōruawairua, Meretoto/Ship Cove and Motuara Island.
Shears said the project, part of a Sustainable Seas National Science Programme, broadly worked on how to better manage the marine environment to “ideally reverse the effects of seaweed loss”, as well as make ecosystems more resilient to future changes. .
He said healthy reefs are generally dominated by large seaweeds and kelp, and have a large number of predators, such as blue cod and crayfish. The reefs also supported diversity and played an important role in carbon recovery.
Scissors showed images of Meretoto/Ship Cove in 1958, which at the time were dominated by large brown seaweeds.
“If we move fast, the reefs are relatively barren and covered in sea urchins,” he said.
“There are a number of factors and stresses that affect the Sounds. Sediment runoff, forestry, long-term overexploitation through fisheries, and on top of that we have climate change.”
He said that in order to understand what caused these losses, a survey was conducted in 2018 using a camera through the Queen Charlotte Sound and part of the Tory Channel.
“What we found was, I think, a little depressing, because large parts of the Queen Charlotte Sound were dominated by cinchona and large seaweeds were missing.
“In the inner and middle parts of the Queen Charlotte Sound, most of the reefs are barren and dominated by cinchona, but as you go into the Tory Channel you’ll see more seaweed and large kelps.”
He said the research found that cinchona emerges as the main factor limiting the kelp forest. A lack of predators boosted the cinchona population.
And while removing cinchona wasn’t a solution in and of itself, it may have been a tool for recovery, he said.
When removing cinchona in the Hauraki Gulf, seaweed was rejuvenated.
Seaweed was low in the inner areas of Queen Charlotte Sound, which was expected to slow kelp recovery. In the outer parts of the sound, for example Motuara Island, there was still a fair amount of seaweed in the shallow water.
At each site, researchers removed cinchona from about an acre of reef. The hedgehogs were the size of a golf ball and therefore not really suitable for kai.
“Understandably, we had to go through a long process to get a permit to do this work and work with iwi.
“What we expect is that these seaweeds will invade the reefs, and we’ll be monitoring that.
“In November, we plan to transplant juvenile kelps so that we can monitor their survival over the summer. We suspect that some species may be quite sensitive, such as the giant kelp.”
After the meeting, Shears said one of the only ways to rebuild the predator population would be to stop fishing.
“Maybe we can remove the cinchona and the kelp will come back, but that will only be the temporary effect unless we can do something else to keep the cinchona numbers in check,” he said.
He said he was really surprised by how quickly the seaweed in the Gulf of Hauraki had come back to life.
“But this is where it will be interesting to see where in a different system, with different stresses, how the reefs react,” he said.
“We have set up locations in the Queen Charlotte Sound under different conditions. We will also look at how the quality of the cinchona changes.”
The study was also part of the University of Auckland student Dallas Lafont’s PhD.
Local Democracy Reporting is Public Interest Journalism funded by NZ On Air