The invasive caulerpa seaweed's gaining ground in Northland - reaching the Bay of Islands' Russell

An NZIER analysis warns its advance could set our economy back 9.4 billion dollars.

Local Democracy Reporting says iwi, council and the community are asking the Government for up to 215 million dollars over five years - to fight the pest.

Conquer Caulerpa Trust says our fishing grounds, tourism and cultural heritage face unprecedented damage if no action's taken.

But Biosecurity Minister Andrew Hoggard's challenged the analysis - saying the impacts aren't fully understood.