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Written By

Rachelle McCabe


College of Science and Engineering

Publish Date

8 June 2024

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Pollution reduction with hungry Blacklip Oysters

Could the humble Blacklip Rock Oyster be the pollution pac-man of our oceans and waterways? ĢƵ Professor Jan Strugnell thinks so and she has the research to back it up. To mark World Ocean Day 2024, the theme of which is Catalysing Action for our Oceans and Climate, we take a closer look at how these munching molluscs could bring about change.

With our oceans under threat from pollution, development and climate change, research like Professor Strugnell’s has never been more important. She recently co-authored a study that examined the effectiveness of using to remove nitrogen, phosphorous, solids and chlorophyll from waterways.

“Oysters feed by filtering the water column and so we knew that they would have some ability to clean it up. What we were really surprised to learn though is how good they were at it,” Professor Strugnell says.

Local studies such as Professor Strugnell’s emphasises that there are many parts to play as scientists across the globe to work to improve water pollution.

As Professor Strugnell says: “The biggest threat to the Great Barrier Reef, after climate change, is poor water quality. Climate change is a global problem, but water quality is a local one and therefore, we can take action locally to improve it,” she says.

Professor Jan Strugnell at work under water.

An undersea solution

Professor Strugnell says scientists have turned their interests to biological filtration methods to clean-up nutrient-rich wastewater in recent years. These methods are a cost-effective alternative to expensive man-made water treatment practices.

She said the organic content of wastewater from aquaculture – such as faecal matter and undigested food – serves as food for oysters, who can also assist in the removal of fine sediments from the water column.

Referred to as , this oyster waterway cleanup process removes environmental pollutants from water biologically. The benefits of this natural process include a reduction in contamination risk; improved waste cleanup efficiency; a decrease in remediation costs; and potential environmental improvements.

“Our study showed the Tropical Blacklip Rock Oyster had filtration rates three to five times faster than other oysters, like Sydney Rock Oysters, and so this suggests they might be particularly well suited to biofiltration roles.”

"The Tropical Blacklip Rock Oyster has several characteristics that suggest it would be well-suited to bioremediatory applications. These include a large size and fast growth rate, and resilience to fluctuations in temperature and salinity."

ĢƵ Professor Jan Strugnell

Professor Jan Strugnell at an aquaculture farm.
An image of oysters plated up.
Left: Professor Jan Strugnell on-site at an aquaculture farm (supplied), right: Her recent research has focused on oysters and how they can clean up waterways.

Cleaning credits promoting sustainable practices

Professor Strugnell teamed up with ĢƵ Masters by Research Aquaculture student for the oyster study. Both were interested in how the characteristics of the Tropical Blacklip Rock Oyster could be effectively incorporated into existing aquaculture processes.

“Ben Rennie was working on several aspects of breeding the Tropical Blacklip Rock Oyster in captivity. He was working on trying to optimise water quality parameters in captivity to get them ready to spawn for aquaculture,” Professor Strugnell says.

“Around that time we were also learning about – these credits turn a unit of nutrients into a tradable unit.”

The Reef Credits scheme rewards land managers for taking action to improve the quality of the run-off from their land into the Great Barrier Reef catchment. When landholders implement approved projects on their land that demonstrate reductions in nutrients or sediments, they generate Reef Credits.

The scheme was conceived after governing bodies recognised an urgent need to incentivise water quality improvements across the Great Barrier Reef catchments. A Reef Credit represents a volume of pollutant prevented from entering the Reef.

Research such as Professor Strugnell and Ben Rennie’s, when considered alongside initiatives such as the Reef Credit Scheme, highlights how scientists, governments and industry leaders can work together to facilitate action on water pollution.

“We were aware of the power of oysters to filter the water column and so we wanted to do some work towards quantifying their ability to clean up the water, with the ultimate goal that oysters might be part of the Reef Credits scheme,” says Professor Strugnell.

ĢƵ Professor Jan Strugnell holds an oyster.
An image of oysters.
Left: ĢƵ Professor Jan Strugnell with a Tropical Blacklip Oyster (supplied); right: oysters close up.

Putting the nutrient chomping oysters to work in the Tropics

Plans are now in the pipeline to move the study onto real life aquaculture farms, with farm-based trials expected to build on the findings of the lab studies.

“A sensible next step in the research would be to deploy oysters in wastewater ponds in prawn and/or barramundi farms,” Professor Strugnell says.

“Initial trials in barramundi farm wastewater ponds were really encouraging. The distribution of the Tropical Blacklip Rock Oysters overlaps with prawns and barramundi farms in our tropical regions.”

As part of the research project, scientists tested Tropical Blacklip Rock Oysters’ uptake of waste over different temperature ranges and with different densities of the animal.

“The findings highlight the effectiveness of the oyster is closely linked to temperature, with 32 degrees Celsius returning the highest filtration rate for much of a five-hour period.”

The findings also indicated that 1.20kg of nitrogen is removed per tonne of harvested oysters. It also seems the oysters remove the most pollutants when immersed in warm tropical waters.

“In 2020/21 the oyster industry in NSW harvested 5081 tonnes of oysters. If tropical oyster production in Queensland grew to this scale it would remove approximately 6098kg of nitogen/year and contribute to a six per cent reduction in total nitrogen/year from aquaculture farms in the Great Barrier Reef catchment,” said Professor Strugnell.

ĢƵ researchers have discovered the humble oyster is a champion when it comes to waterway clean-ups.

Improve water quality, improve the Reef

Improving the quality of our oceans and waterways is key to improving the state of the Reef, Professor Strugnell says.

“An excess of nutrients, like nitrogen, can negatively impact the delicate balance of the Great Barrier Reef and lead to algal blooms, lower coral diversity, increased coral disease and also promotes crown of thorn starfish outbreaks,” she says.

Oyster farms and the introduction of oysters into wastewater outputs of other farms can play a role in removing some of the nutrients that enter the ocean through run off, Professor Strugnell says, with projects like this slotting nicely into World Ocean Day’s Catalysing Action For Our Ocean and Climate .

She notes that spreading the word about research and innovation is also key to promoting action. As a former Editor-in-Chief of , Professor Strugnell has written extensively about her optimism for the future of our oceans despite some pressing key challenges.

“Our research is a little step forward in discovering the power of our local oysters to clean up our waterways,” Professor Strugnell says. “It’s important to highlight our oceans, promote them in the media and reflect upon their importance to our livelihoods.”

Want to know how you can help catalyse action? for more information. You can also explore other exciting Marine Biology and Aquaculture projects happening at ĢƵ.

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