Clammed up: the race to stop NZ’s latest invader
Invasive clams have made themselves at home in the Waikato River. Scientists hope to stop them in their tracks.
In a Hamilton laboratory Dr Michele Melchior is juggling buckets, nets and waders.
The NIWA freshwater ecologist may look like she’s preparing for a field trip, but instead she’s spraying everything with a variety of compounds to find out what will kill something the size of a grain of sand without damaging anything else.
The task is urgent. Right now the official advice to ensure the invasive clam, Corbicula fluminea, doesn’t stray from the Waikato River, is to check and clean boats and gear and then dry everything for 48 hours. That’s a lot of time between fishing trips.
The clam, native to Asia, is one of New Zealand’s newest invasive freshwater species. First discovered in May 2023 at Bob’s Landing, Kārapiro, it has also been found in Lake Maraetai and downstream reaches of the Waikato River, but, touch wood, so far nowhere else.
What makes this invasive species so bad is that it doesn’t need a mate to breed. It fertilises itself and is capable of spitting out a staggering 70,000 clams per year. These baby clams are among the tiniest invisible enemy imaginable – approximately 0.2 millimetres wide.
The clam can live quite happily bunched up with 20,000 others in one square metre for up to five years. Such dense populations have clogged pipes and infrastructure overseas and have the potential to do the same here. The Waikato River, the longest in New Zealand, has numerous drinking water intakes and hydroelectric power plants along its
425 kilometre course.
The clam appears to like the same habitat as the kākahi, our native freshwater mussel, and by sheer weight of numbers could reduce the habitat available for kākahi. The clams also release ammonia. In dense populations those ammonia levels can get high and be detrimental to underwater plants.
Vigilance may be the only control option at the moment, but at their Hamilton base, NIWA freshwater scientists are working quickly to figure out how to get ahead of the clams and stop them establishing further.
Biologist Brian Smith was one of the first people to see the invasive clam – he was called in by Biosecurity New Zealand (Ministry for Primary Industries) when they were first spotted at Bob’s Landing on Lake Kārapiro, and asked to conduct a visual search along the river.
“It was so different from anything else I’d seen. I didn’t know what it was, but I did know it wasn’t supposed to be there.”
He checked several other sites downstream – the Moana Reserve, Keeley’s Park, the Cambridge boat ramp and Wellington Street Beach, in central Hamilton. There were clams at all of them.
“The thing with invasive species is that they tend to do quite well. Without predators or the biological controls they may face in their native habitat, they can quickly take over.”
The next step was a 'delimiting survey' undertaken for Biosecurity New Zealand and starting from Taupō to establish exactly where the clams were, followed by a more comprehensive baseline survey in May last year. By August the clam had been declared an unwanted organism under the Biosecurity Act.
In October the NIWA freshwater science team was notified it had succeeded in securing $10 million from MBIE’s Endeavour Fund to develop “novel control methods, understand the impacts of the clam on taonga species, and predict its further spread”.
One of the most important challenges for the scientists is learning how the invasive clams behave in New Zealand and how they interact with native flora and fauna.
Scientists want to establish where the baby clams are likely to go in the water column when they are dispersed, the quality and depth of water they prefer to establish in and what they’re happy co-habiting with.
As Dr Deborah Hofstra, NIWA’s principal scientist, freshwater ecology says: “At some point we want to know where the clams might be. Are they everywhere or can we say ‘this area is too muddy so put your efforts here’.”
The team is also taking what’s already been tried overseas and adapting it to the New Zealand environment while testing other ideas.
This knowledge will assist in testing conventional control methods and developing innovative approaches aimed at targeting the most vulnerable lifestages of the clam to disrupt its development and limit further spread.
Melchior will trial benthic barrier methods – effectively like laying carpet over the clam habitats, something that has proved successful in controlling the invasive weed Lagarosiphon major in South Island lakes, and more recently to smother exotic caulerpa. Caulerpa is another invasive species, first discovered in New Zealand marine habitats in 2021.
She’s also working with an acoustician based at the University of Waikato to test whether sound could disrupt clam development.
Smith has recently placed passive samplers in the river in different habitats, as part of research to develop a passive sampling method. When he removes them, he’ll count the juveniles as a first step to designing methodology that could be more widely used along the river. This data will ultimately be fed into predictive models.
Meanwhile, NIWA environmental economist Zoe Qu is figuring out how to determine the economic and social impact of their spread.
To attempt this, she needs to first understand the potential economic impact of the clams on people, industries and other end users of the river, and what people think about the clam spreading from their own perspectives.
Meanwhile, businesses are keen for information to assess the risks and work out mitigation options. The clams have already been found in other places, or at least knocking at the gates.
Recently Smith dug his hand into the clear bottom of the Waikato River. As he rinsed off the sand he held out his palm. On it sat eight clams.
AI seeks out invasive species
Pinpointing new incursions of invasive species in marine and freshwater ecosystems is now quicker, cheaper and more accurate
NIWA is leading the way in developing new detection tools that are likely to revolutionise how New Zealand carries out its biosecurity programmes.
Top of the list is using AI in conjunction with underwater drones or autonomous unmanned surface vessels. The work is multi-disciplinary and has involved NIWA aquatic scientists, AI data science specialists and the instrument systems team building the hardware.
That combined expertise has led to a new approach to the detection of three invasive species: Caulerpa and Mediterranean fan worm in the marine environment and Lagarosiphon major in freshwater. Each species is capable of rapid growth and developing dense stands with the ability to displace native biota.
But detecting and managing invasive species in our oceans and freshwater environments is time-consuming and laborious work.
NIWA is contracted by Biosecurity New Zealand, part of the Ministry of Primary Industries (MPI), and Land Information New Zealand (LINZ), to carry out marine and freshwater surveillance surveys using visual surveys by divers or with underwater video cameras filming the seafloor or lakebeds, wharves and other infrastructure. In the past, the video was processed and analysed on shore before decisions were made on how to manage or eradicate the species.
However, in recent months marine ecologist Dr Leigh Tait has been mapping Caulerpa incursions around Waiheke Island and the Bay of Islands using an underwater remote operated vehicle (ROV) in conjunction with an AI detector system. The AI algorithm is trained to recognise Caulerpa and records its position via GPS as cameras pass over it.
This detection in real time is the game changer, according to Tait.
“For a regulatory agency like MPI, we could feed a product like this into a web interface where there are people back in Wellington who are able to see it.
“If, for example, we discover something that isn’t where we expected it to be, we could be given real time instructions on whether to continue to find the edges of the population. It makes things a lot more flexible, more efficient and also reduces the costs of processing.”
The other advantage of this technology is the ability for it to go where divers can’t.
By necessity, underwater surveillance surveys have to be planned to fit within a diver’s safe limits and availability.
“I really believe that is going to be the standard operating style for these types of surveys in the future. These methods are highly accurate, sensitive and provide an immediate geographic location,” says Tait.
“And the thing about the AI detector is that development here and now will be of benefit when the next invasive species arrives and the next one after that."
Meanwhile, NIWA freshwater ecologist Dr Daniel Clements has been leading the freshwater AI detection project and is excited by its potential to limit the spread of other freshwater invasive species.
“It is far more cost effective to conduct management at the early stages of an invasion.”
The lagarosiphon AI prototype has been trialled in several rivers and lakes around New Zealand, and when combined with remotely operated surface vessels will be able to be deployed more frequently and extensively than current surveillance methods. The addition of hydroacoustic sensors into the detection work will further enhance capability.
Dr Graeme Inglis, manager of NIWA’s biosecurity services programme which includes a marine invasives taxonomic service and operational management of biosecurity responses, says the development of practical and efficient techniques for surveillance and management of aquatic pests is one reason New Zealand is a world leader in biosecurity.
“We are one of a few countries to have an active national surveillance programme. Many countries don’t have a government equivalent to Biosecurity New Zealand, that is, an agency with a mandate to manage risks from invasive species.”
He points to New Zealand also being one of the first countries to implement mandatory ballast water control on ships and the first to introduce regulations on ships governing biofouling.
“New Zealanders have a general awareness of the importance of biosecurity to our economy, natural environments and taonga – more so than most other nations. We understand what’s at stake if new pests are not detected and managed effectively.”
But he is concerned that further challenges lie ahead. He is wary of emerging diseases and 'sleeper pests' that may already be present in New Zealand and may become problematic with a warming climate.
In the meantime, work on managing the spread of Caulerpa continues. NIWA’s field teams have been working solidly for the last few years undertaking delimiting surveys throughout north-eastern New Zealand to determine the size of new incursions, and trial control methods with partner organisations, including large-scale application of salt or chlorine, hand removal, benthic matting to smother the plant, and industrial-scale suction dredging.
There have been some successes, and further evaluation is needed to find the right management tool for different locations.
As Tait and Clements continue to refine their AI detection methods, NIWA is focusing on developing the computing infrastructure to allow data scientists to quickly develop algorithms for new species.
That’s because when it comes to biosecurity the only certainty is that pests that are already here won’t stop reproducing without intervention, and the next invasive species is knocking on the door.
SOS: save our shellfish
Dr Henry Lane loves eating oysters – preferably cold, raw and with a dash of lemon.
He also likes them in the lab, where he trades his shucking knife for a microscope to understand hidden threats to our shellfish in a changing climate. Peering into a hidden microbial world, he is investigating the bacteria Vibrio, a pathogen emerging as an issue as water temperatures rise.
Lane, a marine biosecurity scientist, leads NIWA’s aquatic animal health work, a rapidly growing area due to its importance for commercial, recreational, and customary fisheries as well as aquaculture.
Eating raw or undercooked shellfish contaminated with Vibrio can make you sick. But it can also kill shellfish and in a changing climate could become more prevalent in New Zealand waters.
Lane’s project looks at predicting the risk of Vibrio in wild and production shellfish like pipi and mussels, under a range of climate change scenarios. The work draws on field observations and NIWA's extensive climate modelling and environmental data science capabilities to deploy machine learning tools to predict where the risk is highest.
There are increased anecdotal observations that shellfish die-offs are now happening more frequently.
While Lane says there are primary drivers contributing to large shellfish die-offs such as temperature, salinity, or nutrient inputs, we need to understand their relationship to Vibrio and other pathogens in New Zealand’s waters before we can begin predicting them with any accuracy.
“There has been this emergence of a syndrome known as summer mortality, which happens when mass numbers of shellfish die in summer and no one quite understands why.”
A lack of baseline data is now starting to be filled, but Lane says there remains “large unknowns we’re just trying to understand”.
“Once you identify a potential issue, then you can begin to understand it and start to develop some management approaches. Unfortunately, there’s no silver bullet, but the science will provide options to be able to do something about it.”
It’s also biosecurity science that may ultimately see the flat oyster farming industry reinvigorated.
After decimating flat oyster populations in Europe, the parasite Bonamia ostreae turned up in the Marlborough Sounds in 2015. When it was subsequently discovered near Stewart Island, the Ministry for Primary Industries ordered the removal of all flat oyster stocks from marine farms in New Zealand to protect the iconic Bluff oyster fishery.
Lane says the idea was that by reducing the number of hosts of the parasite, you could reduce the opportunities for transmission – similar to how lockdown aimed to prevent the spread of COVID-19.
NIWA has been carrying out surveillance of bonamia in wild oysters for a number of years.
“It’s a wily little parasite. It hasn’t gone away and the wild fishers are incredibly worried about it turning up in their stocks, while at the same time there are people wanting to start farming oysters again.”
Lane believes the research is a chance to show that New Zealand can have its cake and eat it.
“I do see this as an opportunity to demonstrate that we can have a productive wild fishery that is safe and secure as well as an aquaculture industry.”
The key to that is minimising the risk of transmission between farmed populations and the wild.
“The research needs to be data driven and that’s one of the things I’m trying to do right now.
“Because if we’re realistic, things are going to continue to turn up in New Zealand and we can’t just keep destroying our aquaculture industry.”
NIWA's 30 years of aquatic biosecurity
- 1995 - NIWA scientists establish the first NZ Ballast Water Advisory Group to develop strategy on managing risks from ships’ ballast water and biofouling.
- 2001 - NIWA begins surveying marine plants and animals in ports and marinas to provide baseline monitoring of native and introduced organisms.
- 2002 - NIWA implements a national surveillance programme for high-risk exotic marine organisms. It becomes the National High Risk Site Surveillance programme in 2005.
- 2002 - NIWA uses DNA methods to identify the invasive Japanese paddle crab, Charybdis japonica from Waitematā Harbour.
- 2004 - NIWA undertakes a biofouling risk study on 500+ international vessels to support NZ’s Craft Risk Management Standard for vessel biofouling.
- 2005 - NIWA undertakes a national delimitation survey at 26 high-risk locations for Unwanted Organism, Styela clava, following detection in Auckland and Lyttelton.
- 2005 - NIWA expertise sought for possible foot-and-mouth outbreak on Waiheke Island to predict wind and atmospheric conditions.
- 2006 - NIWA provides expertise to help mitigate spread of invasive algae didymo, discovered by a NIWA scientist in the Waiau River.
- 2007 - NIWA advises on containment of lagarosiphon, a weed threatening hydro-generation. Meanwhile, NIWA identifies the best formula to kill didymo.
- 2008 - NIWA detects the Unwanted Organism Mediterranean fanworm in Lyttelton Harbour and leads a local elimination programme.
- 2013 - NIWA works with Zespri and Plant & Food Research to develop a model to forecast risks from the kiwifruit disease Psa-V ahead of weather-related outbreaks.
- 2015 - NIWA awarded $3 million from MBIE’s Environmental Research Fund to develop methods to forecast and quantify the impacts of invasive marine species.
- 2016 - NIWA leads a project to enhance collaboration in marine biosecurity with Australia, Canada and the US, involving scientists from more than 50 institutions.
- 2017 - NIWA provides crucial expertise after discovery of the lethal parasite Bonamia ostreae at two Stewart Island oyster farms.
- 2017 - NIWA conducts critical modelling to assess the potential sources and timing of risk for aerial transport of Myrtle Rust spores from Australia.
- 2021 - NIWA responds to the discovery of two new species of the fast-growing invasive seaweed Caulerpa by conducting surveillance and research.
- 2023 - The invasive freshwater clam Corbicula fluminea discovered in the Waikato River. NIWA begins surveys along the river.
- 2024 - NIWA is awarded $10 million from MBIE’s Endeavour Fund to develop clam control methods.