Māori concepts of environmental guardianship will feature at the International Seaweed Symposium 2023, highlighting a New Zealand program to control invasive seaweed that is threatening local ecosystems.
By Catherine Norwood
The depths of winter might not seem ideal for diving off the southeast coast of Aotearoa, New Zealand’s South Island (Te Waipounamu), where water temperatures drop to bone-numbing 8°C degrees.
But divers from Ngai Tahu, the Iwi (Māori tribe) with the largest rohe moana (marine area) in New Zealand, are gathered for a week spent out on and in the water. The nutrient-rich winter months provide the best time to remove the invasive seaweed wakame (Undaria pinnatifida) from their local waters.
Wakame is farmed extensively in its native region around Japan, South Korea and China and is widely used as a food ingredient. However, the species is an unwelcome invader in New Zealand.
Wakame’s incursion into New Zealand waters has been expanding since the late 1980s.
Marine scientist Dr Chris Hepburn says it now threatens the future of native seaweeds, as well as the native marine and inshore wildlife that relies on those seaweeds. Hepburn is a Professor at the University of Otago at Dunedin and leads an ongoing research collaboration with Ngāi Tahu, called Te Tiaki Mahinga Kai.
The partnership integrates customary knowledge with scientific approaches to support Ngāi Tahu leadership in the restoration of its customary marine and aquatic resources in Te Waipounamu.
And wakame is firmly in the sights of Ngāi Tahu Tangata Tiaki (customary fishery managers). Hepburn says extensive stands of wakame are now established around much of New Zealand’s coastline, expanding out from port areas. Surveys of more than 100 sites within Mātaitai and Taiāpure Customary Protection Areas in 2021 demonstrate the dominance of this invasive species in Te Waipounamu.
The species is benefitting from a range of pressures that have already contributed to the decline of native kelp reefs in the past 20 years, including rising water temperatures and sedimentation. Wakame is resilient to a wider range of water temperatures than the native kelps.
Ecosystem impacts
In recent years when marine heatwaves have killed off native kelp reefs, wakame has invaded the vacant space, effectively out-competing the kelps and preventing them from re-establishing. High sediment loads in coastal waters resulting from sediment and nutrient runoff also block the light that native kelps need to grow, and further favour the more adaptable wakame.
Although wakame is also a kelp it simply can’t perform the same role in local ecosystems that native species such as bull kelp (Durvillaea spp.) and giant kelp (Macrocystis pyrifera) play. Dr Chris Hepburn
“Wakame is an annual and our native kelps are perennials, so it does not provide the same kind of year-round habitat because it dies off in spring,” Hepburn explains. “It is not as large as our kelps. It only grows to 2 metres. Giant kelp grows to 25 metres in New Zealand. That’s a much-reduced area of habitat in the water column for fish and for rock lobster larvae, and other creatures to safely hide and grow in.
“And it doesn’t float. Both bull kelp and giant kelp float because of the bladders they produce. Because they float, our native kelps wash up high on beaches, and this beach wrack is an important part of the food chain for many shore-based species. Birds feed off the wrack, including the iconic flightless kiwi on Rakiura (Stewart Island).
“Undaria sinks so less washes up, and this can impact on where the wrack goes, also impacting on key customary species such as pāua (abalone) that rely on drift kelp as a source of food.” Pāua, he says, are often found in specific aggregations related to drift seaweed availability which can be very patchy. This is an example of wakame's significant and interconnected impacts on the local ecosystem.
Ngāi Tahu are concerned about these long-term impacts and are leading a program with the support of Hepburn and his team at the University of Otago to remove wakame from their local waters, where they can.
Although there are conflicting views in the scientific community about the value of control programs, Hepburn says such programs have been effective in specific areas, allowing native species such as bull kelp and giant kelp to re-establish.
“If we prioritise the areas where we want to see control, such as the Customary Protection Areas which have special significance for Ngāi Tahu, that is at least a start.”
Wakame sales fund control
As part of the new control program, Ngāi Tahu have secured New Zealand’s only control permit to harvest wakame from natural substrates for commercial sale. Being a control program, however, they can’t make any profit from the sale of the harvest. Instead, the sales revenue is channelled back into further control efforts, funding ‘kaitiakitanga’ – their customary principle of guardianship, or environmental stewardship.
The control program kicked off for the 2022–23 season in August with the team of newly trained Ngāi Tahu divers taking to the waters of southern Te Waipounamu. Given the existing markets for wakame, Hepburn is confident the program will successfully fund itself.
“Ultimately, our success is in the people we work with, empowering coastal communities and supporting their restoration of productive coastal ecosystems. Learnings from wakame control could provide a platform for a native seaweed industry that is built off the principles of kaitiakitanga and guided by Ngāi Tahu leadership that builds the wellbeing of our coastal communities,” Hepburn says.
The involvement of First Nations people in ocean stewardship and commercial opportunities in the seaweed sector will be discussed at International Seaweed Symposium in Hobart, Australia and online from 19-24 February 2023. Professor Chris Hepburn will be a keynote speaker at the symposium.
Visit ISS2023 for more information about the symposium program, keynote speakers and registration.