An invasive seaweed in the North Island can't be eradicated using half measures

Exotic caulerpa has formed dense mats across the seabed in multiple sites including the Bay of Islands, Mahurangi Harbour, Waiheke Island and Great Mercury Island.

It smothers native plants and disrupts the fragile marine ecosystem.

Ngati Manuhiri Settlement Trust CEO Nicola MacDonald says there's a number of ways to remove and eliminate it.

She says there are mat liners which suppress the light and suffocate the weed, hand removal and vacuum suction dredging.