Biosecurity agents hope the discovery of fanworms at Tutukaka Marina doesn't mean the tide has turned on efforts to keep the highly invasive pest out of Northland waters.

Experts are cautiously optimistic one of Northland's most iconic coastal areas may have escaped a potentially disastrous invasion despite the recent find of three juvenile Mediterranean fanworms on boats and marina structures.

As well as the potential for fanworms to wreak havoc on the coastline's ecosystem, the find is at the launching pad to the world-renowned Poor Knights Islands Marine Reserve.

The fanworm (Sabella spallanzanii) forms dense colonies that could affect native and farmed species such as mussels and oysters by competing for food and space. Dense colonies could also change the underwater scenery of an area.

Advertisement

They can live in tidal mud or sand, on rocks and marine structures such as wharf piles. They have stiff sandy tubes, up to 40cm long, formed from hardened mucus secretions, and a two-layered crown of feeding tentacles which can retract into the tube.

The latest extensive search at the marina was sparked by the find of a heavy infestation on a boat in Tauranga that had spent nine months at Tutukaka. That boat had earlier been in Auckland, where the fanworm infestation has been described as out of control.

The Northland Regional Council (NRC), Ministry for Primary Industries (MPI) and Department of Conservation joined forces to respond to the local threat from the species, which hitchhikes on the bottom of boats.

Irene Middleton, NRC aquatic biosecurity specialist, said results from the Marine Invasives Taxonomic Service confirmed the Tutukaka specimens were too immature to have reproduced.

"However, we will need to wait until spring to resurvey the marina to ensure divers have not missed any young worms, which, if present now, would simply be too small to be seen with the naked eye," Ms Middleton said.

The Tutukaka discovery is the first time fanworms have been found in Northland outside Whangarei Harbour, where the pest was first seen in 2012.

Jeroen Jongejans, from Dive!Tutukaka, said it was a reminder for everyone to be vigilant - skippers in carrying proof of their vessels' anti-fouling history and marina managers in carrying out the required checks.

Mr Jongejans said Northland authorities were being proactive about fanworm, a species very hard to contain because of the mobile nature of commercial and recreational boating. He said the infestation was so bad in Auckland, "they have just given up".

"It is not a losing battle up here but all of us need to co-operate. It's about becoming aware of the problem and staying on top of it."

Mr Jongejans said little was known about the effect a serious incursion might have on an area like the richly bio-diverse Poor Knights environment.

"The great thing about the ocean is that it's pretty good at looking after itself. There are areas that are far more susceptible than others to harm by invasive species."

He said the seeming inevitable arrival of fanworm was "part and parcel of the ever changing environment. Like possums and rats on land they'll find their niche. You try to contain and control and minimise".

Next summer the regional council will increase dive checks of boats in Northland waters, targeting one area or harbour at a time and issuing inspection proof for boaties to carry.