Aotearoa’s waterways are under pressure from one of the most serious marine biosecurity challenges of our time: the rapid spread of caulerpa, a highly invasive tropical seaweed that threatens native ecosystems, marine food chains and coastal livelihoods. First detected in New Zealand waters in 2021, caulerpa has now established itself in multiple coastal areas, prompting rāhui, fishing and anchoring restrictions, and urgent efforts from iwi, communities and agencies to contain its spread.
Native to warmer tropical seas, caulerpa species such as Caulerpa brachypus and Caulerpa parvifolia grow rapidly on seabeds, forming dense carpets that smother native seaweeds, shellfish beds and seagrass habitats. Once established, these mats outcompete local marine life, disrupt fish nurseries and reduce biodiversity, putting pressure on kaimoana and coastal ecosystems that have sustained tangata whenua for generations.
Among the most significant areas now affected are Kawau Island and Little Barrier Island (Te Hauturu-o-Toi) – both part of the traditional rohe of Ngāti Manuhiri. These are two of at least 11 locations where caulerpa has taken hold in the Hauraki Gulf and surrounding coasts, underscoring how far and fast this pest can spread.
Listen to the full interview with Nicola MacDonald – Chief Executive of the Ngāti Manuhiri Settlement Trust – here:
https://waateanews.com/2025/11/25/nicola-macdonald-chief-executive-of-the-ngati-manuhiri-settlement-trust/ (waateanews.com)
In that kōrero, MacDonald describes why caulerpa is such a concern for coastal iwi and communities – not just as an environmental pest but as a threat to te taiao, kaimoana resources, cultural values and future generations’ access to healthy marine ecosystems. She explains that dense mats of seaweed can overgrow once-vibrant seafloor habitats and make it harder for native species to survive and thrive.
The seaweed’s spread has already led to biosecurity measures, including Controlled Area Notices that restrict activities such as anchoring and fishing in infested waters to reduce unintentional transport of fragments on vessels and gear – one of the key ways caulerpa moves from place to place.
Iwi and regional partners have also implemented rāhui (traditional bans) alongside legal controls, reflecting a combined tikanga and science-based approach to protect precious moana.
Scientists and biosecurity experts warn that without swift and sustained action, caulerpa could continue to expand its reach, potentially affecting more of Aotearoa’s waters and altering marine environments in ways that could take decades to understand or mitigate. National strategies now include prevention, detection, removal, research and coordination – but many iwi leaders say this effort must be matched with adequate resourcing and community involvement to safeguard their rohe moana.
Efforts to halt the spread of caulerpa today are about protecting both ecological integrity and cultural connections to the sea – ensuring that future generations may continue to draw sustenance, identity and connection from healthy coastal ecosystems.
Stay tuned to Radio Waatea’s #SummerSeries for further updates on environmental kaupapa and how whānau across Aotearoa are responding to shared challenges.
