Invasive clams litter Karapiro beach

Thursday, 8 June 2023

Niwa researchers use bathyscopes to look for invasive golden clams.

Some are the size of a fingernail, others a bottle cap, and at one Karapiro beach golden clams are now so numerous they’re difficult to miss amongst the sand.

On hand at Bob’s Landing to catalogue the unfortunate find on Wednesday were Wellington based aquatic incursion investigators from the Ministry of Primary Industries, colleagues from Niwa and a representative of South Waikato iwi Ngāti Raukawa.

Armed with kick nets, sieves and trays, Josh Wardle of MPI and his team had located dozens of clams within minutes of arriving at the banks of the Waikato River.

Empty golden clamshells. Some specimens range in size from several millimetres to several centimetres.

Those found would be sorted, kept damp, bagged in ziplock and returned to MPI’s animal health lab in the Capital for further testing, he explained.

”Essentially we’re just getting a few more samples, the response that’s been stood up to deal with this involves engaging quite closely with the iwi. So we’ve got one of the iwi reps here. Today was catching up with them, showing them what they[the clams] look like, showing them how we do the sampling, so they can get involved and look out for them in different areas in the river,” Wardle said.

Josh Wardle, right, looks on as Niwa colleague Brian Smith displays a find.

That sampling process involved scooping buckets of river sediment into sieves of different sizes, eventually leaving only the clams. Then, wrapped in damp kitchen towels, the bundles of clams were put into polystyrene boxes for transport south in the check-in luggage of MPI staff.

“Today was also about getting a few more samples to take back to Wellington just so we can run some tests on them to make sure there’s nothing fishy with them. We’ve done some testing on previous samples and didn’t find anything. We just want to corroborate that and make sure there’s nothing else they might carry.”

As the officials went about their work in waders, passersby at the purportedly scenic reserve were obliviously to the potential environmental disaster unfolding in front of them.

At one point during the collection, a late model Jaguar sporting gold rims arrived to treat the researchers to a series of haphazard donuts in the gravel.

Niwa environmental researcher Ngahuia Herangi searches the shore.

Using bathyscopes (underwater viewers) Wardle and the team could quickly locate batches of the clams. A seemingly easy task given the quantity.

Not only would general surveillance by the public be an important element in the battle against the clam which can outcompete native freshwater mussels and clog water intakes, but so too would the use of environmental DNA(ENDA), Wardle said.

“We are developing a targetted EDNA assay. It’s environmental DNA, so it’s like DNA that is shared,” he explained as two French tourists enjoyed a late lunch outside their rented campervan.

“It's the same with things that are in the environment. If we can develop what is called a targetted assay, so essentially we collect DNA from the clams and make sure it's in reference databases, then what we can do is use EDNA kits.

“We suck up the water, put it through filters, and it leaves the DNA behind, then you take that, analyse it at the lab and compare it to databases that confirm a match to say whether that animal is there.”

The burgeoning field which is particularly useful in biomonitoring and security, does have imperfections though, Wardle says.

“It’s quite difficult, it’s quite a new technology, so there are a lot of caveats to it. You can get false positives, false negatives, so you’ve got to a lot of testing… It’s just about getting on the ground and having a look.”