A small infestation of invasive exotic Caulerpa seaweed has been discovered and treated at Smugglers Bay near the entrance to Whangārei Harbour, prompting renewed calls for vigilance from boaties, fishers and divers.
The approximately one-metre-wide patch was identified by Northland Regional Council divers conducting routine marine biosecurity surveillance alongside the Department of Conservation. Subsequent testing confirmed the seaweed was exotic Caulerpa, an invasive species already established in parts of the Bay of Islands.
Northland Regional Council says the discovery demonstrates the value of ongoing marine monitoring and the importance of having specialist dive teams capable of responding quickly to emerging threats.
Following the detection, council staff launched an immediate response operation using a benthic mat treatment with chlorine applied beneath the mat, a recognised method for containing and eradicating small infestations.
Authorities say rapid intervention is essential because exotic Caulerpa can spread easily through tiny fragments, allowing it to establish new colonies in previously unaffected areas.
Follow-up surveys of surrounding waters have so far found no additional signs of the invasive seaweed. However, further monitoring and surveillance will continue as a precaution while agencies assess the effectiveness of the treatment.
Biosecurity experts believe the discovery is most likely the result of human-assisted spread, as Caulerpa is not known to travel long distances naturally. Fragments can be unintentionally transported on boat anchors, anchor chains, fishing gear and diving equipment.
The council is encouraging anyone using Northland’s coastal waters to inspect equipment carefully before leaving a site, remove any attached seaweed and dispose of it responsibly on land to prevent it re-entering the marine environment.
Local leaders say the swift and coordinated response should provide reassurance to the community while highlighting the importance of collective action in protecting the region’s harbours and coastal ecosystems.
Northland Regional Council is working closely with Biosecurity New Zealand, the Department of Conservation, local hapū and iwi on ongoing surveillance and response planning.
Members of the public who believe they have seen exotic Caulerpa are being urged to report sightings immediately to Biosecurity New Zealand.
The latest detection serves as a reminder of the growing biosecurity challenges facing Aotearoa’s marine environment and the importance of early intervention to safeguard culturally, environmentally and economically significant coastal areas.
