The exotic seaweeds Caulerpa brachypus and Caulerpa parvifolia have been found in waters at Aotea (Great Barrier island) and Ahuahu (Great Mercury Island). These exotic seaweeds can spread rapidly and could affect native taonga species. Ngāti Hei asks residents and visitors to Te Tara-o-te-Ika-a-Māui / Coromandel to do their bit to stop the spread.
What is exotic Caulerpa and where did it come from?
Caulerpa brachypus and Caulerpa parvifolia are seaweeds exotic to Aotearoa / New Zealand. They are native to the Indo-Pacific region, ranging from Africa to Australia, the Pacific Islands, and southern Japan.
Both of these exotic Caulerpa seaweeds are closely related and appear identical. They have fronds up to 10 centimetres long that rise from long runners or roots known as stolons – the marine equivalent of kikuyu grass. It is not known how long these two Caulerpa species have been here or how they arrived. It is possible the two different seaweeds were carried together by a visiting international vessel or on a domestic vessel from another, as yet unidentified, infested area of Aotearoa.
They can be found growing below the tideline at between 2 metres and 30 metres on both hard surfaces and in sandy areas.
We have our own native Caulerpa species but they look quite different (see identification guide below).
How big a problem is it?
In favourable conditions, Caulerpa can spread rapidly, forming vast, dense beds or meadows, both smothering and displacing our native taonga species like our own algae, including our native Caulerpa, and shellfish.
NIWA have surveyed the outbreaks in Aotea and Ahuahu and conclude that, as of August 2021, Caulerpa had extended over significant areas in Blind Bay / Okupu (88Ha), Tryphene (2.3Ha), Whangaparapara (0.5Ha) and Western Bay Ahuahu (3.2Ha).
How it spreads
Exotic Caulerpa can be spread through breaking into little pieces. This can happen due to wave action, but the biggest risk of spread is when it gets stuck on equipment, like anchors or fishing gear, and is moved to new locations that way. Fragments can survive out of water for up to a week or more in moist locations.
What is being done
Biosecurity NZ is working closely with mana whenua and the local communities, along with Auckland Council, the Waikato Regional Council, and the Department of Conservation. It’s not too late to fight back, but at this point our best hope is early detection to stamp out spread to other areas while more research is conducted on how to tackle the larger areas.
How you can help
Keep an eye out for Caulerpa. If you come across beachcast Caulerpa, or see it out snorkelling, diving or fishing then report it immediately.
Boaties: Make yourself aware of the restrictions on anchoring placed by MPI/Biosecurity NZ. This means knowing where the outbreak is and the rules around anchoring and fishing in these areas. Check your gear – anchors and chains especially. If you see any seaweed on your equipment, chuck it straight back.
More info
Visit Biosecurity NZ’s Caulerpa page www.biosecurity.govt.nz/caulerpa
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