An international search has begun to identify a mysterious marine animal that threatens New Zealand's biosecurity after infesting Whangamata Harbour.

The Ministry of Fisheries is investigating the sponge-like creature because of fears that it could spread with devastating effect on the aquaculture industry.

There has been huge interest in the animal since harbourmaster Merv Martin saw it growing on piles at Whangamata wharf.


When scientists could not identify the animal, samples were sent to an international expert in Queensland.

Californian scientists asked for samples after reading about its discovery in Weekend Herald internet reports.

There has also been a reported sighting of the creature in Auckland's Waitemata Harbour. Media interest has extended to the BBC, American agencies and even Aftonbladet, Scandinavia's largest daily newspaper.

The parasitic sponge-like animal kills sea life when it embeds itself on a surface.

It does a "double-invasion". First, it settles on a spot, beginning life "filter-feeding" on plankton and smothering its hosts.

Then it peels away and starts the "second invasion", fixing itself to the clean surface and developing into thick, matted flat sheets.

The Environment Waikato regional council commissioned marine scientist Dr Brian Coffey to study the animal's "pest potential". He raised fears that it could spread through a mussel farm or something similar, destroying crops.

The ministry this week used his report in assessing the animal's biosecurity risk.

There have been other similar invaders, such as a mystery swimming crab plaguing flounder fisherman in the Waitemata and now in the Firth of Thames and the Chaetopterus worm, whose dense mats briefly threatened the South Island scallop industry.

The chief technical officer for marine biosecurity, Dr Chris O'Brien, said the new invader would be monitored but little could be done until it was identified.

"If it starts to move, then we will start to talk about how to stop it."

It may have already moved. Aucklander Fred Symes believes he saw an identical creature on a buoy rope at Little Shoal Bay on the Waitemata.

But with thousands of species resembling the mystery animal - temporarily dubbed Didemnum sp.? - exact identification is virtually impossible until it has been properly researched.

So far the quest has gone from Whangamata to Dr Coffey then to Te Papa museum marine scientist Dr Rick Webber, who has not seen anything like it before.

The creature then baffled a National Institute of Water and Atmospheric Research scientist, Mike Page, who passed it to Dr Patricia Mather at the University of Queensland.

She has studied sponges from the tropics to Antarctica and expects to finish her assessment soon.

Until then it will not be known whether it is an evolution of an existing native sponge, an overseas pest that has stowed away or a new animal.