On the hunt for marine pests - Reotahi Marine Reserve snorkel survey

The annual hunt for marine pests was on recently in Whangārei Harbour's Marine Reserve at Reotahi. Staff from Northland Regional Council, Experiencing Marine Reserves charity and students from North Tec and Kamo Intermediate school took part in this year’s Reotahi snorkel survey.

Staff from Northland Regional Council, Experiencing Marine Reserves charity and students from North Tec and Kamo Intermediate took part in this year’s Reotahi Snorkel Survey. The event is organised by the regional council’s Marine Biosecurity team.

The Reotahi Snorkel Survey is a good opportunity for Northland Regional Council’s Marine Biosecurity team to monitor the presence and spread of marine pests in the marine reserve and to educate people in what to look for when out in the ocean.

Kathryn Lister, the council’s Marine Biosecurity Manager, says among a range of unwanted marine nasties snorkellers were looking specifically for the Mediterranean fanworm (Sabella spallanzanii) and Undaria Seaweed (Undaria pinnatifida).  They can be found in the shallows of the marine reserve and on artificial structures in the area.

The Mediterranean fanworm is native to the Mediterranean and Atlantic coast of Europe. It was first detected in New Zealand in 2008. It’s now present in a number of New Zealand harbours including Whangārei in Northland. It was detected in Opua in 2018 and NRC are attempting to eradicate from there.

“Mediterranean fanworm can form dense colonies that can outgrow native species and interfere with the natural biological processes of an area,” says Ms Lister.

The ability of the species to attach to a wide range of surfaces in varying environmental conditions, its fast rate of growth, and its prolific breeding habits, make it particularly competitive. The presence of the Mediterranean fanworm in areas where mussels or oysters are located may affect their growth due to competition for food.

 “Vessel hulls are the most common way for marine pests to hitch a ride from one place to the next and fanworm spread easily in the waters of Northland because it is warmer here,” says Ms Lister.

Northland’s coastline and rich, diverse marine life is part of our identity as a region, but an increase in boat movements has seen a rise in marine pest spread.  Although Mediterranean Fanworm is already here, Kylie Pedersen, Marine Biosecurity officer was pleased with the outcome of the snorkel day.

“Although we found a few fanworm (14), they didn’t seem to be in abundance, nor did it appear that there were more than last year.”

Samples of the fanworms were bagged up and taken back to the lab at Northland Regional Council’s offices for research purposes.

“We’re also pleased that we didn’t find any evidence of Undaria Seaweed (Undaria pinnatifida) in the area,” says Ms Pedersen.

Undaria Seaweed grows on any hard surface including shells, reefs, ropes, wharf piles, vessel hulls, moorings and other artificial structures. It can form dense "forests" in sheltered reef areas.  The impacts of Undaria Seaweed are not well understood and are likely to vary depending on the location. It can change the structure of ecosystems, especially in areas where native seaweeds are absent.  The weed also has the potential to become a nuisance for marine farms by increasing labour and harvesting costs due to fouling problems.

Ms Pedersen, Marine Biosecurity Advisor at NRC says that everyone has a role to play in managing the pathways through which marine pests can be spread.  In the case of Mediterranean fanworm, that is usually via fouling on boat hulls.

“Clean and check your boat,” she urges, “and report any marine pests that you find.”

Advice for boat owners, and links to local marine biosecurity rules, can be found at