WSP ecologists discover invasive freshwater clam

Working on a stretch of the Waikato River near Lake Karāpiro, the pair stumbled across a bed of odd-looking shellfish – which later turned out to be the highly-invasive gold clam (Corbicula fluminea) - also known as the Asian clam or golden clam.

“As part of an ecological assessment for a project, we were investigating the riverbank at Bob’s Landing. We were only there for a couple of minutes before we saw some shells in the water we couldn't identify,” says Alex.

“There are some native species of clam [in the area], but they have a small not ridged shell. We knew immediately we were looking at something strange.”

Alex and Mark contacted Michael Winterbourn, an emeritus professor at University of Canterbury, who directed them to Australian Museum shellfish specialist Winston Ponder.

“[Winston] identified the genus and said it was likely to be a fluminea species. We contacted Biosecurity New Zealand and sent them a live sample. They sent it to Te Papa where specialists identified it as Corbicula fluminea.”

Biosecurity New Zealand and freshwater experts from NIWA then headed out and assessed the species distribution. The clam was found one kilometre upstream and forty-five kilometres downstream of where Alex and Mark first spotted it.

Shortly after, the Ministry for Primary Industries (MPI) issued a public advisory.

The rapid reproductive ability and build-up of large populations of the clam poses a threat to hydroelectric power plants, water treatment plants, and water intake pipes. They can potentially compete with native species for food. Their invasive nature has been difficult to control and eradicate overseas.

“Properly cleaning gear is crucial to prevent the spread of pests like these in waterways,” says Alex.

“It’s important to follow MPI's check, clean, dry protocols when using gear in any waterway, especially for shellfish where treatments like heat treatment, freezing, disinfectants, and steam cleaning are recommended to kill organisms.

“If you think you've seen the clam, you should note the location, take a photo if possible, and contact Biosecurity New Zealand as soon as possible.”

Working with mana whenua, Waikato River Authority, Waikato Regional Council, Department of Conservation, Land Information New Zealand, and other organisations, Biosecurity New Zealand is now trying to determine more about the clams’ spread and explore potential future actions.