Anyone that’s been diving on the eastern coast of Tasmania is all too aware of the damage that the longspined sea urchin has wreaked on our reef habitat and kelp forests. But did you know that a by-product of harvesting the invasive species for their roe could play a beneficial role on Tasmanian farms?
Researchers at the Tasmanian Institute of Agriculture (TIA) are contributing to control efforts by assessing the benefits of using urchin processing waste as a soil ameliorant for the agricultural industry. This circular economy research is led by Research Fellow, Dr Harriet Walker.
“Harvesting and processing urchins for high end restaurants and export markets is the most effective control measure for invasive sea urchins. However, this results in a large amount of waste with 90% of the urchin diverted to landfill at a substantial cost to industry,” Dr Walker said.
“We wondered if the waste from urchin processing was actually a waste product, or if it was a product that we just hadn’t found a use for yet. Joining forces with the Institute for Marine and Antarctic Studies (IMAS), we identified an opportunity to use this waste product in the agricultural industry which is more profitable than disposing it onto a paddock or into landfill.
“The agricultural industry is seeking organic and effective alternatives to synthetic inputs to boost crop productivity, so this is well worth exploring.”
IMAS researcher Dr John Keane added: "Longspined Sea Urchins have extended their range into Tasmania with climate change. With rapid population growth we now have over 20 million urchins on our east coast reefs, resulting in 15% of the reef area becoming unproductive urchin barrens.”
"If we can turn the waste generated from urchin processing into something valuable like soil ameliorant, we can help address this environmental issue and increase the financial viability of the industry."
Dr Walker said there was potential to transform urchin waste into a fertiliser or liming product that could be made commercially available to agricultural growers and home gardeners.
“Through previous trials we’ve learnt that ground, dried urchin waste is effective as a liming product. It is very high in calcium which is an important nutrient for deacidifying soils. It also contains key micronutrients such as boron and iron,” Dr Walker said.
Previous trial work was funded by the Fisheries Research Development Council.
A current project funded by the Marine Bioproducts CRC and the Tasmanian Government involves long-term field trials at a commercial vineyard, an organic apple orchard, and potato trial at the TIA Vegetable Research Facility.
A vineyard trial was established at Two Bud Spur vineyard in Southern Tasmania and involved control plots with no treatment, a commercially available lime product, a coarse sea urchin waste application, and a fine sea urchin waste application.
Results from the vineyard trial found that soil pH was persistently increased using sea urchin waste application, resulting in greater soil pH change longevity than the commercial liming product. Significant differences in yield and grape composition have not yet been observed through this trial.
“We had a soil pH challenge at our vineyard and saw an opportunity to collaborate with Harriet and the team by offering eight rows for a commercial scale trial. This allowed us to assess the real-world impact of sea urchin fertiliser on our soil,” Dr Craig Mundy, IMAS Research Fellow and owner of Two Bud Spur vineyard, said.
“We were pleased to see that the urchin waste effectively increased soil pH levels, and importantly, there were no issues with salt content which is a key consideration for soil health.
“Sustainability is a priority for our vineyard, so the opportunity to use a locally sourced, repurposed fertiliser is highly appealing. Reducing our ecological footprint while improving soil health is a win-win.”
The potato trial at the TIA Vegetable Research Facility in North-West Tasmania involved varying levels of sea urchin waste including no application, 4 tonnes per hectare, 8 tonnes per hectare, and 12 tonnes per hectare.
“We found the soil pH level was higher at the time of harvest but there were no differences in yield parameters. The trial will be repeated in the 2024/25 season, and it will also be considered as part of a new zero net emissions demonstration farm which is being established at Forthside in mid-2025,” Dr Walker said.
Dr Walker is also investigating the impact of the urchin waste on soil health at the long-term sites through chemical, physical and microbiological changes in the soil.
This is the last season of this trial and harvest for apples and grapes will occur during April and May, with the potato trial to be harvested in winter. Final data collection will happen later this year ahead of the conclusion of the project at the end of 2025.
Dr Walker and Dr Keane are working with industry in an attempt to commercialise the product, utilising not only sea urchin waste, but waste from the entire seafood sector.