Aussie predator makes itself at home in Whangarei Harbour

It's Australian, is a bottom dweller with a ravenous appetite, a dangerously competitive streak and can move twice as fast as its New Zealand counterparts.

No it's not a cricketer - it's the tiny Australian dog whelk which is invading the Whangarei Harbour and inter-tidal areas as far south as the Firth of Thames. Infestations of the predatory gastropod molluscs have been found in the eastern Auckland coastal belt but the population is described as exploding in sheltered Whangarei Harbour and estuarine areas.

The rapidly increasing presence of the Aussie invader has marine biologists worried it will compete for the same food and eventually swamp the population of the bigger, slower native whelks. The dog whelk is also known to eat the native species.

Auckland Museum research associate Margaret Morley plans to study the population in the Whangarei Harbour where it appears to be settling in faster than elsewhere.

The adults are only 10mm across and, using a scent gland, can track food from more than 10 metres away. They feed on sick or dead marine life by grinding it up and then sucking it through a feeding tube. In turn, the whelk is a main food for bottom-feeding fish such as snapper and tarakihi.

Niwa sea floor ecology biologist Michael Townsend said: "Bio-invasion is always a hot topic because of the potential for harm.

"The question is, now what will happen and what can be done?"

Two shells of the species were found in the central Waitemata Harbour in April 2009, and one live specimen was found near Henderson Creek, further in-harbour.

Small populations were found in June 2010 during a Niwa survey carried out on behalf of the Auckland City Council.

"It may have arrived as juveniles on a boat hull or in seawater ballast but soon it was appearing at multiple sites in the same harbour," Dr Townsend said. "It had established quite quickly in sandy mudflats and inter-tidal areas."

Where geographical remoteness once provided protection, infestations were now aided by the shorter commuting times for ships. Meanwhile, Australian marine biologist Kirsten Benkendorff is testing antibiotic compounds from the whelk which appear to be active against certain cancer cells and are non-toxic.

There are also indications the whelk could provide muscle-relaxant properties. However, claims of its cancer-curing properties may be premature. Dr Benkendorff told a conference in Canberra last year that a viable medication would be unlikely within six years.