He said TTR was vague in how big the area was it would mine.
But 3-5 million tonnes of core iron ore was expected to be sucked from the seabed creating a dead zone down to a depth of 20-45m for 20 years, he said.
Mr McCabe said the Government scientists from Niwa were six months into a four-year study of the seabed to "enable the management of offshore mining".
"It would be a giant open-cast mine under the sea, and it's our future they are messing with for three per cent of the profits."
Opunake High student Marlene Ruka told the meeting she had just finished a biology paper that looked at seabed mining.
"People lack the understanding of the environmental and social impacts and how this will really affect us as people."
In her paper, she said the proposed economic wealth of seabed mining was a key factor that contradicted the environmental issues.
Opunake High deputy principal Andrea Carr said seabed mining would compromise tourism.
"The west coast is a unique area and people want to come here. It would ruin the future potential of this area."
Te Runanga o Ngati Ruanui deputy Tumu Whakaae, Ngapari Nui, addressed the meeting and said the iwi had been challenging TTR for information.
"No way will they be able to start until we get this information on our seabed. We are protecting this for our mokopuna, for the future."
Brian Broughton, who lives at Patea Beach, said he saw seabed dredging on television.
"What will happen to the silt? We will have a bigger problem. We won't get employment. It won't be here. They will bring the experienced people in from New Plymouth."
Mr McCabe told the meeting KASM had been asking for a breakdown of jobs.
"Jobs will be created ... but in China, not here in Patea.
"For every 10 tonnes of seabed that would be sucked up, nine tonnes would go back into the water and smother everything below.
"The west coast is a dynamic coastline 24/7. The mining will block the light, and phytoplankton relies on the light for photosynthesis. This would affect the whole food chain."
A man who identified as a diver said he did not want foreigners taking their sand.
"When Waipipi Ironsands was here, boats came in from overseas. Now there are tropical fish that should not be down there."
Tennille Snooks from Hawera said it was a "no-brainer". "It's got to affect our coastline. It will kill the west coast."
Egmont Plains Community Board member Sharon Arlidge said she was nervous that the TTR proposal was being done on modelling: "There is nothing on the scale they are proposing that has been done in the world."