The dire state of the marine environment off Coromandel Peninsula will be the focus of a hui in Whitianga this afternoon.

Conservationists, iwi leaders and fishers are meeting to discuss issues such as fishing, pollution and climate change, which are putting heavy pressure on marine ecosystems on both sides of the peninsula.

Last month, divers could only find one legal-size scallop per 26 square metres of the seabed in some parts of Ōpito Bay.

A rāhui was placed on the scallop beds last December.

Scientist and hui organiser Thomas Everth says many other species, such as crayfish, were under threat.

Visible sea life in Coromandel waters had declined markedly in the last 25 years, Everth says.

"When you look at the number of fish boil-ups or the size of those... or the number of birds working them, that has all been declining significantly in the 25 years that I've been sailing here," he says.

"It's really, really worrying.

"If this trend continues we might find that we are tipping some tipping points in our marine environment."

The coast was "fundamental" to Coromandel communities and the reason many residents lived there, Everth says

Ngāti Hei kaumātua Joe Davis, marine scientist Tim Haggitt and Hauraki Gulf Forum chief executive Alex Rogers will speak this afternoon.

All are welcome at the hui from 3pm to 5pm at the C3 Church Hall in Whitianga.

-RNZ/Sam Olley.