Whenuakura Marae is one of 12 Nga Rauru Kiitahi marae in South Taranaki opposing ironsand mining off the Patea coast.
The marae sits on the boundary of Nga Rauru Kiitahi and Ngati Ruanui and affiliates to both iwi.
Trans Tasman Resources (TTR) has applied for a 20-year licence to mine an area of 65 square kilometres, 22 to 36kms offshore in depths of 19 to 42 metres.
The plan is to mine up to 50 million tonnes of seabed material every year, down to 11m beneath the seabed using screening and grinding processes. But of the 50 million tonnes, only 10 per cent is expected to be titano magnetite concentrate; the remaining 90 per cent will be pumped back into the sea as thick slurry.
Whenuakura spokeswoman Anne-Marie Broughton says the application states that it is "assumed complete de-faunation" will occur.
"In other words," Mrs Broughton said, "extermination of all seabed life."
"The plumes will have smothering and visibility effects on habitats and marine life. There is no known certainty regarding the short and long-term impacts of the activity and, therefore, risk of irreversible damage is a real possibility.
"The 12 marae are horrified that the pursuit of profit for overseas investors is being given priority over the health and wellbeing of our country's marine environment.
"The stealth tactics, speed and dubious modelling of proposed effects should have all New Zealanders very, very worried."
The people of the South Taranaki marae say this type of operation has never been done before.
"In fact, Namibia has placed a three-year moratorium on seabed mining to allow sufficient time for robust environmental assessment.
"Their government states that seabed mining cannot happen if there is not solid proof that it will not have negative impacts on the environment.
"Whenuakura Marae applauds Namibia's standpoint and believes New Zealand must take the same position."
Mrs Broughton said TTR has no proven track record in seabed mining and intends using methods that will create long sediment plumes north and south of the mining site.
Hearings before the Committee of the Environmental Protection Agency opened in Wellington on March 10 and hearings are expected to start in Taranaki on April 28.