1000-plus fanworm removed in latest Opua eradication bid

7 Oct 2019, 9:23 AM

A close-up of one of the Opua fanworm recovered earlier this year.  The image shows the fanlike crown of feeding tentacles that extend out of its tube, giving the fanworm its name.

A close-up of one of the Opua fanworm recovered earlier this year. The image shows the fanlike crown of feeding tentacles that extend out of its tube, giving the fanworm its name.

More than 1000 unwanted Mediterranean fanworm (Sabella spallanzanii) have been pulled from the water in and around Opua Marina in the latest search and removal operation by specialist divers.

Northland Regional Council Biosecurity Manager Don McKenzie says favourable conditions meant a several-strong contract diver team had been able to carry out 20 straight days of search and removal operations over winter.

“Visibility was favourable and remained within the minimum requirement of 500 millimetres in and around the marine throughout the jointly-funded regional council and Biosecurity New Zealand dive effort.”

Mr McKenzie says divers have been targeting the fanworm since contractors discovered a single specimen of the marine pest while working in the Opua area in winter last year.

The August dives were the latest in a series as part of a stepped approach to try and remove the pests.  Under that approach, divers carry out a removal operation and then stand down while the results and associated data are examined by biosecurity experts and the best management approach is decided on.

“Our councillors felt strongly that the Bay’s importance across multiple fronts – including environmentally, economically and culturally – meant they couldn’t pass up what may still prove to have been our only real opportunity to eradicate fanworm there.”

“But with both the council and Biosecurity NZ already having collectively contributed several hundred thousand dollars to the removal efforts, “essentially, we’re reviewing the situation very carefully as we go to make sure it makes practical and financial sense to continue.”

The first stepped response had been competed in late April, yielding 267 fanworm, with the second step – which traversed a more targeted area – resulting in 1013 individual worms removed in the 20 days to 27 August.

Of those removed in August, 90 percent (913 individuals) were from artificial structures, eight percent (85 individuals) from the seafloor and of the remaining handful recovered, a dozen individuals had been removed from moorings and three from reefs.

Mr McKenzie says the recovered worms typically ranged from just 30mm to more than 400mm but with an average of about 120mm.

The maturity, numbers of fanworm and their spread has reinforced earlier indications they may have been in the area (probably having hitchhiked in on a visiting vessel with a dirty hull) for several years.

He says the results of the latest operation had already been reported to key stakeholders and regional councillors had also been kept abreast of developments including an update at a recent monthly meeting in Whangarei.

A decision on whether to continue the operation via a third step – likely to cost about $100,000 – was expected shortly.

Mr McKenzie says in the meantime, authorities are continuing to urge people in and around Opua in to ensure they do what they can to avoid spreading fanworm.

“It’s vital boaties ensure their vessel and any associated equipment – moorings and their rope/chain and fishing nets – is clean and free from fouling which may contain marine pests like fanworm.”

A large, tube-dwelling worm, Mediterranean fanworm is the largest fanworm in New Zealand, with a body up to 20mm wide and 800mm long.  It has a prominent crown of fan-like feeding tentacles (up to 150mm wide) extending out of the tube. The crown is often banded orange, purple or white. Tubes are leathery, flexible and muddy-looking and they are generally found on hard, sub-tidal structures, but can also be buried up to 10cm deep in soft substrates.

Fanworm is unwanted because it can quickly form dense colonies, forcing out native species and interfering with their ability to feed and breed.  (Sabella have also been found growing on scallops in Whangarei Harbour and have the potential to spread onto other shellfish, including farmed species.)

“Under regional council rules, it’s an offence to transport marine pests in Northland.  Vessels entering Northland and moving between harbours must have no more than ‘light fouling’ on their vessel.”

(‘Light fouling’ is classified as a slime layer and/or barnacles, and up to five percent ‘macrofouling’.  ‘Macrofouling’ is large, distinct multicellular organisms visible to the human eye like barnacles, tubeworms, or fronds of algae, but importantly permissible macrofouling excludes pest species, including Mediterranean fanworm, clubbed tunicate and the Asian kelp ‘undaria’; these may not make up any of the 5% allowable macrofouling.)

With the warmer summer months looming, Mr McKenzie urges people encountering marine pests to notify the regional council as soon as possible by phoning (0800) 002 004 or emailing [email protected] or by calling Biosecurity New Zealand’s Pests and Diseases hotline on (0800) 809 966.

“It’s important that you don’t try and remove any fanworm you may discover yourself as this must be done by authorised personnel,” he says.  “This is because fanworm need to be removed intact and can spawn under stress.”

“If you see a Mediterranean fanworm or suspect it on your hull, structure or substrate, please take a photo and call or email us with the location.”

Information on a range of marine pests can be found at www.nrc.govt.nz/pestcontrolhub or www.marinebiosecurity.org.nz

The council’s rules and marina requirements can also be found at www.marinepests.co.nz