Boaties, fishers, beachgoers - here’s how to help.
Aucklanders call their hometown the City of Sails – but it’s not just about yachts. Kayaks, tinnies, jet-skis, ferries, divers, and other water lovers flock to the Hauraki Gulf and the thousands of beaches and coves around the region.
Now, skippers and crew are being recruited to form a Dunkirk-style small-boat armada to repel an alien invader threatening our marine playground. And not just those out on the water: dog-walkers, beach strollers, and anyone who visits the coastline can lend a pair of eyes too.
The uninvited visitor is exotic caulerpa, a species of fast-growing, invasive seaweed first reported off Aotea Great Barrier Island in 2021.
It has now spread beyond the Hauraki Gulf into the Bay of Islands and Coromandel, usually in popular anchorages, according to Liz Brooks, Auckland Council’s team manager Pathways and Marine. No stranger to biosecurity campaigns, her 30-year CV includes senior roles with the Department of Conservation and Motutapu Restoration Trust.
Exotic caulerpa has the potential to blanket the seafloor, smothering native seaweeds such as seagrass. It can disrupt the habitats of fish, shellfish and other marine life, leading to less biodiversity and threatening access to some of our most cherished marine spots.
And boaties, divers, marine farmers and visitors, including tourists, could lose access to these gems if they must be declared off-limits for anchoring, leisure or aquaculture. Controlled Area Notices (CANs) are in place at Aotea (Great Barrier Island), Ahuahu (Great Mercury Island), and Te Rāwhiti (Bay of Islands), while rāhui have been established at these locations as well as Waiheke. Boaties should check official updates before heading out, as restrictions may change.
The public is the first line of defence, Brooks says. They’ve tipped off officials about the arrival and spread of caulerpa a number of times. “The first reported sighting at Aotea was posted on the iNaturalist (citizen scientist) site by a member of the public, and it was quickly picked up and identified.
“It was growing under people’s noses but nobody had actually realised it was a different or a new seaweed. When MPI (the Ministry for Primary Industries, responsible for protecting Aotearoa from biological risk) surveyed the coast, they found a number of sites in just a few days.”
Same with Rawhiti: “That was from a local kaumatua who was walking along the beach and recognised he’d come across something we’d never seen before.” And Waiheke, where members of the public have reported finds near Onetangi and Oneroa, the island’s most popular anchorages.
“When you think of the number of people who are out on the water or at the beach – fishing, diving, walking the dog or just looking at the view – it’s really important for them to keep an eye out. If they see something that doesn’t look familiar, to take a good photo and send it in, along with the location. We can follow up and investigate it. We can’t be everywhere ourselves, so we really do need the public to help.”
Brooks says council, government and a wide range of experts are still trying to get a good measure of exotic caulerpa’s impacts on the gulf and other coastal areas in the region.
“Obviously there could be quite a big impact on commercial ventures such as fisheries and shellfish – for example, if the snapper population is diminished because there is less area or a suitable habitat for them to spawn, and it’s been detected growing near mussel farms.
“In terms of recreational fishing, diving and tourism, it might start to have an impact on how people can undertake those activities, especially if there are constraints on where they can go, where they can fish and where they can anchor.”
That’s not just threatening fun on a sunny summer afternoon: fish, shellfish and enjoying the seashore are extremely important in the life of many cultures who have made their home in and around Tāmaki Makaurau.
Brooks says caulerpa can’t survive in depths greater than 50m and is considered to be “negatively buoyant”, meaning it sinks. However, it is turning up where Kiwis take their boats and gear, and where they take their boats and gear to next.
It’s easy to accidentally pull caulerpa up on an anchor chain, so cleaning the boat and gear is vital (see tips below). There’s plenty of it, too – one infestation was described as being like underwater tumbleweeds in an old Western; another time, a whopping 500kg was attached to an anchor chain.
How you can help
Boaties, fishers and beachgoers – you can help contain the spread of exotic caulerpa if you:
- Avoid anchoring or disturbing the sea floor in infested areas. Anchors, chains and fishing/diving gear can break up caulerpa and pieces get snagged, accidentally moving it to new locations.
- Always check and clean gear: anchors, fishing gear, dive equipment and any other gear when moving between regions.
- When at sea, check your anchor, chain and equipment for any attached seaweed. If you find any, bag it and bin it onshore. If you can’t do this, return it to the waters it came from; do not move it to a new location.
- On the beach or in the water, if you see any unfamiliar seaweed, take a photo, record the location, and report it to MPI on 0800 80 99 66.
- Respect Controlled Area Notices (CANs) and rāhui. They’re in place to protect vulnerable marine environments and help prevent the spread. Avoid affected areas whenever possible.
For more information go to ourauckland.nz/stopthespread