A marine invader found in the Far North could already be spreading throughout the country with mussel spat, according to Biosecurity New Zealand.
The sea squirt, called pyura, is firmly entrenched at Ninety Mile Beach, where mussel farmers from around New Zealand get spat to stock their farms.
MAF Biosecurity NZ surveillance
manager Brendan Gould said pyura may have already been distributed to other areas with the mussel spat.
The impact it could have on marine life is so far unknown.
A non-poisonous species, pyura praeputialis forms extensive mats, up to 20cm deep, that overgrow mussel beds and other native intertidal life.
But they are not considered as big a threat to aquaculture as the club sea squirt.
Pyura was first discovered near Cape Maria van Dieman by Auckland-based marine scientist Bruce Hayward of Geomarine Research in 2007 but other priorities prevented Biosecurity NZ dealing with the problem.
Staff were at the time involved with the didymo scare, club sea squirt infestations, sea squirts in Opua as well as a Mediterranean fan worm infestation in Lyttleton, Mr Gould said.
In October last year MAF staff spent a week investigating how far the pyura infestation had spread over 200km of coastline from Herekino Harbour around the cape to Houhora Harbour.
Known as "delimiting', the survey found a further 21 infested sites from the two or three known sites at the tip of the Aupouri Peninsula three years earlier.
It has not been established whether the sea squirt has moved south of the investigation area.
Next month marine scientists would analyse the data collected by Biosecurity NZ staff and decide the best form of attack against the Australian invasion.
"In terms of trying to eradicate them, you can't just go and aerial spray them or just pull on your gumboots and pick them up," Mr Gould said.
"There's a lot of potential impacts it could have but it's uncertain whether it will cause damage or die away in a few years. It's hard to tell."
Large populations of pyura have been found in Chile where it has displaced native species.
