Hundreds volunteer to move invasive caulerpa marine weed from Bay of Islands cove

Hundreds lent a hand to clear caulerpa from Ōmākiwi Cove in the Bay of Islands.

Hundreds of volunteers rolled up their sleeves over Easter to help clear a Bay of Islands cove of caulerpa, known as one of the world’s most invasive seaweeds.

Kaitiaki Arana Rewha estimates around 500 tonnes of the title="https://www.nzherald.co.nz/northern-advocate/news/caulerpa-seaweed-bay-of-islands-anchoring-ban-now-in-place-to-fight-threat/3X5I5ODPYZBNRIIWNXCGGZFGGY/">thick, exotic seaweed were moved from the beaches at Ōmākiwi Cove to above the high tide line in four days.

Ōmākiwi Cove, in Te Rāwhiti, is ground zero for New Zealand’s mainland infestation of caulerpa, where it was first spotted in May 2023.

Since then, the pest has spread to dozens of other Bay of Islands locations, with anchoring bans and removal trials in place to help stop the spread.

Te Rāwhiti locals were buoyed by all the volunteers coming to help, says Arana Rewha, also known as Rana.

But when ex-tropical Cyclone Tam battered Northland with hurricane-strength winds – up to 156km/h was recorded at Cape Rēinga on Thursday – and waves up to 12m high, hundreds of tonnes of caulerpa were washed up on Bay beaches.

Rewha – who was the first to identify caulerpa on the mainland – said locals felt despondent when they first saw how much of the seaweed had washed up at Ōmākiwi Cove.

But when a call for volunteers went out, hundreds of people from all over Northland volunteered to help with the clean-up, held from Friday to Monday.

Hundreds of tonnes of caulerpa washed up on Bay of Islands beaches during ex-tropical Cyclone Tam.

“All the crew felt a bit odd when they first saw how big it was. But all through the clean-up, it was laughing and chatting – it was really cool,” he said.

“Because so many people came to help, they are getting to understand [caulerpa]. They 100% came because they felt they were doing something to help.”

The aim of the clean-up was to move the invasive seaweed from the shore – where the tide and currents could then spread it around – to an area above high tide, where it could be left to dry out and die.

About 500 tonnes of exotic seaweed caulerpa were moved from the beaches at Ōmākiwi Cove to above the high tide mark.

The resulting dead seaweed will have to be removed at a later stage.

Rewha estimates more than 300 tonnes of caulerpa were moved from the main beach at Ōmākiwi Cove and a couple of hundred more from a second beach.

The clean-up was led by hapū members from Ngāti Kuta and Patukeha, and representatives from Conquer Caulerpa, members of iwi Ngātiwai, locals like the McConnell family and other volunteers.

Rewha said hapū and iwi now want better plans in place when severe weather is forecast, such as people ready to respond.

They would also like to see more urgency from the Ministry for Primary Industries in managing the invasive seaweed, including better communication with locals on the ground.

Denise Piper is a news reporter for the Northern Advocate, focusing on health and business. She has more than 20 years in journalism and is passionate about covering stories that make a difference.