New study models NZ habitats most vulnerable to Gold Clam invasion  

A new study has modelled which habitats in Aotearoa New Zealand might be most vulnerable to Gold Clam invasion in the hope that management efforts can be targeted effectively. The findings suggest that the highest risk areas are mostly located in Te Ika-aMāui (North Island), in particular, northern Waikato, Auckland, Northland, Bay of Plenty and Hawke’s Bay. In Te Waipounamu (the South Island) areas with the highest habitat suitability included Marlborough, North Canterbury and Christchurch.

The Gold Clam (Corbicula fluminea) is a highly invasive freshwater mollusc, which was detected in Aotearoa New Zealand in 2023. Currently, it has only been observed in the Waikato catchment, but there is significant concern it will spread across the country. The paper’s lead author, University of Otago student Rose Somerville, completed the study alongside Cawthron Institute freshwater scientists Dr Calum MacNeil and Dr Finnbar Lee while on placement at Cawthron as a summer scholar.

Somerville said there is an urgent need to identify suitable habitat for the species beyond the Waikato, given the high probability of spread.
“Our aim was to use modelling to identify habitats in different parts of Aotearoa New Zealand that would be the most suitable for the Gold Clam to thrive in by looking at environmental variables associated with the species’ distribution here and in other parts of the world where it lives,” Somerville said.

“We looked at environmental variables such as temperature, slope, elevation, the sand content of the river/lakebed, and the pH of the water.
“The value of using a statistical model is it gives us a bit of a head start on the invasion. By identifying freshwater habitats with similar conditions to those where the Gold Clam occurs internationally, we can allocate resources to high-risk environments.”

Somerville said it’s also important to note that these predictions are based on past climatic conditions and do not account for future climate change.
“Worryingly, we found temperature to be a key driver of habitat, with the Gold Clam preferring warmer waters, suggesting that climate change may result in more of the country becoming suitable habitat for the Clam.”

Dr Calum MacNeil, an invasion ecologist at Cawthron Institute, said the Gold Clam is a major threat to Aotearoa New Zealand’s freshwater ecosystem health.

“Because it’s a recent arrival, the long-term impacts of invasion are yet to be determined, but there’s a lot of evidence to suggest Gold Clam could outcompete other species including our native freshwater mussel species the Kākahi.”

“Beyond the damage to ecosystems, Gold Clam has also been reported to cause damage to infrastructure by biofouling things like water treatment systems and power plants.”

Freshwater ecologist Finnbar Lee said the study suggested our focus should be on preventing the species from gaining a foothold in new habitats.

“Eradication is a very difficult task once the species has established, so we should focus on preventing it from spreading in the first place,” Lee said.

“Our study only considered where the Clam is most likely to spread, but another important consideration is how the Clam may move between catchments, for example spread via fishing gear, boats or trailers.

“Identifying the potential dispersal pathways between catchments will further inform where management should be targeted.

“We hope this study helps to direct and inform monitoring and management in areas where it’s most needed and look forward to sharing these results with environmental managers and biosecurity organisations.”

Rose said she was thrilled to have the opportunity to publish a research paper during her period as a summer scholar at Cawthron.

“I am very grateful to Finn and Calum for their endless support and encouragement – it was a fantastic opportunity to apply new skills to an important and current topic.”

“The Cawthron summer scholar program has enabled me to get my foot in the door of scientific research in Aotearoa which can be difficult to do coming straight from a Bachelor of Science. I recommend this program to any and all young scientists who are looking for some experience and advice.” 

View the paper here > Full article: Habitat suitability of Aotearoa New Zealand for the recently invaded gold clam (Corbicula fluminea) (tandfonline.com)

View more information about Gold Clam in Aotearoa New Zealand > Exotic freshwater clams (Corbicula) | NZ Government (mpi.govt.nz)