Research on options to manage the invasive Longspined Sea Urchin (Centrostephanus rodgersii), has identified using sea urchin waste as a soil conditioner.
Developing markets for the Longspined Sea Urchin is the leading strategy in Tasmania to control this invasive ocean species. Sadly, it has decimated kelp forests and seabed habitats for high-value species such as rock lobsters and abalone in Tasmania and Victoria through range extension.
In recent years seafood processors in Tasmania have worked hard to develop markets for sea urchin roe (the inside portion of Longspined Sea Urchin) to strengthen the business case for harvesting urchins.
The roe, or ‘uni’ is a delicacy in Asia, particularly China.
Roe accounts for only eight to nine per cent of the animal’s weight – so once the roe is harvested hundreds of tonnes of Sea Urchin waste remains.
‘Waste not’ solutions
This has prompted FRDC-funded research (2019-128) to investigate more productive and profitable uses for the waste, and follows an earlier FRDC-funded project that identified potential uses in agriculture (2016-208).
This project involves a collaboration between seafood processor True South Seafood in Tasmania, researchers at the Tasmanian Institute of Agriculture (TIA), the Tasmanian Abalone Council and the Tasmanian Department of Natural Resources and Environment.
True South Seafood, at Electrona south of Hobart, has processed 600 tonnes of urchins in the past year, generating about 540 tonnes of urchin waste.
Rather than dumping that waste into landfill at a cost of $200 a tonne, it has turned to the ‘urchinator’ – the nickname company staff have given to their waste processing machine imported from China in 2020 to process urchin waste.
Working with the Tasmanian Institute of Agriculture researchers, True South Seafood has modified the machine to improve its efficiency in grinding and drying urchin waste to provide a consistent granulated byproduct.
Crop scientist for the Tasmanian Institute of Agriculture, Dr Harriet Walker, has been testing this in a range of agricultural trials. Sea urchin waste is high in calcium, comparatively high in nitrogen compared with similar marine-based products and high in micronutrients, including boron. Its product profile also meets Australian standards for composts, soil conditioners and mulches, including for certified organic farming systems.
Crop impacts
The project first trialled liquified urchin gut waste as a frost protectant for fruit trees, but this proved unsuccessful. The salt content was too high even when the solution was significantly diluted.
Harriet says other trials conducted between 2021 and 2023 have focused on the potential of the dry, granulated product as a soil conditioner or fertiliser, applied with fine or coarse particle size, and at low, medium and high rates.
To date, the powdered urchin waste has been tested in greenhouse trials on sunflowers, beans and rocket, and in field trials on grapevines, apple trees and potato crops.
In greenhouse trials with potted plants, the product showed a fertiliser effect, but soil conditions in the field are more complex, says Harriet, and it has been more difficult to detect benefits to mature vines and tree crops. “The potato trial in northwest Tasmania might show more of a fertiliser effect because it’s an annual crop, but the data is still being analysed,”
Post Doctoral researcher at University of Tasmania, Harriet Walker, and Technical Officerr Paola Campus, at the University of Tasmania, Paolo Campus, discussing the setup of the sunflower Sea Urchin Waste plant growth trial within the Tasmanian Institute of Agriculture glasshouse.
A vineyard at Gardners Bay is the main site for soil conditioning trials, with the product applied at rates of 10 and 20 tonnes per hectare. The main field fertiliser trial has been undertaken at the R&R apple orchard at Ranelagh, with product applied at rates of up to 12 tonnes per hectare.
Liming effects
“The sea urchin waste is 35 to 40% calcium, which generates a liming effect, and this is overshadowing any kind of fertiliser effect in field trials at this point,” says Harriet.
Liming is a process used to improve productivity of acidic soils in agriculture systems. Benefits from liming include healthier plant roots and more efficient plant growth.
In the vineyard trial, urchin byproduct improved soil pH level by at least one full pH unit. This compared well with the commercial liming products in the trial. A positive liming effect was also reported at the apple orchard trial, although the targeted fertiliser effect was not evident.
“It’s probably not going to be a stand-alone fertiliser product; I see its value more as a soil conditioner – essentially a liming product with added nutrients. And the smaller the particle size, the more rapid the soil improvement effect is,” says Harriet.
While the costings for a commercial product are still being developed, the urchin byproduct has many positives from a marketing perspective which, Harriet says, have also made it a satisfying project to be part of personally.
“As an agricultural scientist, it’s been fascinating working with the seafood sector to develop and trial a new product that could help reduce reliance on either synthetic fertilisers, or on liming products which are the result of energy-intensive mining. We’re value adding to waste to create a product that is recycled and reused, supporting a sustainable product and sustainable farming practices.”
Pictured: Technical Officer, Paolo Campus, taking soil cores (samples) at the vineyard field site
Expanding markets
At True South Seafood, Chief Executive Officer Mark Allsopp expects the next 12 months to be exciting for the company, with new markets for both urchin roe and urchin soil treatment. He says sales of roe will be expanding from Asia into the EU and US in coming months. There is also interest from organic olive and apple producers in the waste byproduct as a soil conditioner.
“We also have interest in the liquid product for use in seaweed aquaculture – that’s a use where the salt levels in the liquid won’t be an issue,” Mark says.
In Tasmania, support for the harvesting of Longspined Sea Urchins will continue to be through the Abalone Industry Reinvestment Fund (AIRF) until 2025. The AIRF is a public-private partnership of the Tasmanian Abalone Council, Tasmanian Commercial Divers Association, Tasmanian Government and Institute for Marine and Antarctic Studies.
Mark expects the state’s urchin harvest will continue to grow over that time.
“But really, we need to invest in post-harvest processes and product development to ensure sea urchin harvesting is commercially sustainable without subsidies. This project is a commercial solution to help optimise the value from the urchin waste,” he says.
Related project
Project 2019-128
This relates to R&D Plan Outcomes 1
