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Environment

Let the facts be a part of the solution

You would consider yourself lucky if you were found alive 24 hours after falling overboard from a boat.
 |  The Informer  | 

The feather-like Caulerpa quickly smothers the sea floors.

In January, a Tairua local, Will Fransen, was fishing solo out behind the Alderman Islands. Somehow he fell overboard and in little over 24 hours drifted in the currents to Mayor Island, over 55 km away. Incredibly for him and his family, he was found alive.

If the currents and tides can carry a human this far, imagine the distance a small fragment of invasive seaweed can spread on the same currents, particularly because the tides and currents flow day in and day out.

It may be easy to point the finger at boaties and blame vessels and marine equipment for Caulerpa’s rapid infestation across the Hauraki Gulf, from Kawau to the Mercury Islands, but we need to take a holistic look at the issue. While human behaviour undoubtedly makes a difference, our impact pales in comparison to the impact that billions of gallons of water travelling up and down the coast have on the spread of Caulerpa.

Caulerpa eventually settles on the seafloor, posing a danger to benthic sea life in the warmer parts of New Zealand, in waters 40m or less, and is toxic to many fish and critters.

This raises an alarming question. What will happen to fish relying on the seafloor ecosystem for their food if it is smothered by an invasive seaweed?

Exotic caulerpa was first found in New Zealand in July, 2021at Aotea Great barrier Island which is a Hauraki Gulf island. It has since been discovered at Ahuaha Great Mercury Island, Te Rawhiti Inlet in NOrthland, Kawau Island, Waiheke Island, Mokohinau Islands, Rakino Island and Fantail bay, Coromandel Peninsula.

The secret to Caulerpa’s ability to spread over such vast distances is pretty simple.

Caulerpa relies on the currents and tides to determine where it settles. In suitable conditions, wave action breaks off small fragments which are deposited in new areas where it then establishes. This natural reproduction process is called fragmentation. Interestingly, it is nearly identical to how juvenile scallops ‘spat’ disperses. It is strange that MPI’s previous recommendation under the previous government was, to ‘throw it back.”

In areas once occupied by scallop beds, Caulerpa can now be found as it benefits from the same currents for dispersal. Great Mercury Island is a prime example. Where the vigorous currents once facilitated the settlement of scallop spat. Today, these historic scallop beds are now home to Caulerpa.

Craig Thorburn, a member of the Waiheke Marine Project Steering Committee and Trustee of Kelly Tarltons Marine Wildlife Trust, has been actively involved in the Caulerpa scene. He was one of the first people to notice that the facts were not adding up.

“After frequently surveying the main anchorages at Waiheke and not finding Caulerpa, we researched its [Caulerpa] natural dispersal processes. We realised that the weed spreads along the currents similar to scallop spat.  Applying this logic, we dove in  a historic scallop bed at Waiheke and found Caulerpa immediately”. This means places like Opito Bay are also at risk of infestation.

Ngāti Hei and the wider community have consistently led the charge in Coromandel, establishing rāhui for scallops then Pink maomao when the Ministry of Primary Industries failed to take action.

But we can’t face this alone. It will take a village to combat Caulerpa, and without support from the government, efforts to control the invasive weed will fall short.

Continuing to present incomplete or misinformation is also frustrating the community’s valiant efforts. Little progress to combat or even appropriately monitor the spread of Caulerpa has been made. Monitoring efforts need to be refined and the main currents and tides need to be a bigger part of the consideration. Where do we start? Easy, with historic scallop bed sites.

Finally, it is still important that we all play our part in preventing further spread and respect restrictions and Controlled Area Notices (CAN) on anchoring and fishing in areas infested with Caulerpa.

If you find yourself out diving, fishing, or walking along the beach and spot Caulerpa, please bag it up and report it to phone 0800 80 99 66.