Whangapoua Harbour declared free of sabella

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Published: 24/10/2025

Whangapoua Harbour, on the eastern coast of the Coromandel Peninsula, has officially been declared free of the invasive Mediterranean fanworm (Sabella spallanzanii) following five years of sustained surveillance.

Waikato Regional Council conducts dive surveillance to determine the presence and extent of marine pests throughout the Coromandel Peninsula and Waikato’s west coast. This surveillance focuses on high-risk areas such as the hulls of moored and berthed vessels, artificial marine structures (marinas, wharves, jetties and moorings), popular anchoring spots and marine farms. 

Sabella is formally designated as an unwanted and notifiable organism under the Biosecurity Act.

It was first found in Whangapoua Harbour on the hull of a vessel alongside the wharf in August 2018, and a single fanworm (220 millimetres) was subsequently found and removed from beneath the wharf in June 2020.

Since then, annual surveillance has been carried out with no further detections. Under best practice for marine incursion management, an area is declared free of sabella after five consecutive years without detection.

Waikato Regional Council Marine Biosecurity Officer Dave Pickering said the result for Whangapoua reflected a strong partnership between the council, Biosecurity New Zealand and the Bay of Plenty Regional Council dive team, whose swift actions and subsequent ongoing surveillance efforts were essential to the surveillance programme.

“Sabella poses a significant risk to New Zealand’s coastal environment,” said Dave.

“It forms dense colonies that compete with native species such as scallops, for food and space. Sabella also biofouls boat hulls, marine infrastructure and can negatively affect aquaculture operations, for example, by growing in high numbers on mussel farm lines.

“Early detection is key because, once established, sabella is extremely difficult to eradicate from an area.”

Like many marine pests, sabella is often spread by infested boats.

“Vessel owners are critical partners when it comes to coastal biosecurity,” says Dave.

“Last year, five vessels were discovered with sabella on their hulls during our dive surveys in Whangamatā Harbour.

“Thanks to the cooperation of their owners, all the vessels were hauled out and cleaned, preventing further spread. Early detection and quick action in these cases made all the difference.”

The council started its marine biosecurity surveillance programme in 2017, particularly to target sabella and clubbed tunicate (Styela clava).

Sabella was first found inside Coromandel Harbour on the hulls of two Auckland-based barges in 2013.

With Whangapoua Harbour now confirmed sabella free, maintaining this success will rely on continued vigilance from the boating community.

Vessel owners are urged to regularly clean and antifoul their hulls and report any unusual marine pest sightings to Biosecurity New Zealand on 0800 80 99 66.

For more information on marine pests and vessel fouling, visit:

Sabella can biofoul boat hulls, and this is how it is often spread.

Mediterranean fanworm (Sabella spallanzanii)