Exotic Caulerpa Response

Caulerpa is a family of seaweeds. In Aotearoa New Zealand we have native species of Caulerpa, but two pest species, Caulerpa brachypus and Caulerpa parvifolia are new arrivals and a serious problem. They are considered ‘Unwanted Organisms’ under the Biosecurity Act September 2021, and hence they’re being referred to as exotic caulerpa to set them apart from our native seaweeds. The classification as an Unwanted Organism means that special permission is needed to handle and remove them.

Exotic Caulpera was first discovered in New Zealand in Blind Bay, Aotea in 2021 and has been since discovered in areas of the Hauraki Gulf and Bay of Islands. Refer to Biosecurity NZ for latest information on the location of exotic Caulerpa.

These exotic Caulerpa species are native to the Indo-Pacific region, ranging from Africa to Australia, the Pacific Islands, and southern Japan. They most likely arrived as a stowaway on a boat anchor or anchor chain.

Caulerpa brachypus and Caulerpa parvifolia are closely related and appear identical. They have green fronds up to 10 centimeters long in the shape of oar blades that rise from long runners or roots known as stolons. They can be found growing below the tideline at between 2 meters and 30 meters on both hard surfaces and in sandy areas. When established, exotic Caulerpa can cover large areas of the seafloor in dense mats.

Exotic Caulerpa can grow quickly and form large dense mats across the seafloor which smother photosynthesising plants and suffocate filter feeding animals that other marine life depend on. It is displacing fisheries resources, and threaten biodiversity.

Experience in the Mediterranean with Caulerpa taxifolia has seen a 30% reduction in biodiversity and a 50% reduction in fish biomass in 6 years[1]. This sort of damage would be devastating for the Hauraki Gulf, which is already under significant pressure. The area at risk is currently considered to be the top of the North Island down to the Bay of Plenty.

Because exotic Caulerpa spreads by fragmentation (it can spread by seed too!) you have to be really careful when removing it. Overseas experience has been that small areas can be treated with benthic mats. Chlorine pumped under the mat, or in the form of pool tablets, is sometime used to accelerate die off. Larger infestations will need to be treated with vacuum dredging. A vacuum dredging trial is currently underway in Aotea Great Barrier and up at Omakiwi Bay Bay of Islands.