The analysis found it would cost $131 million to conduct a full cull of urchins in all reefs over 3291 square kilometres, but this would bring a benefit worth $144 million. If only the most crucial reefs were culled of urchins, at a cost of $43.9 million, benefits worth $92.1 million could be achieved.

Among benefits the study’s authors based their analysis on were the productivity of fisheries and the renewed ability of kelp species to store carbon, nitrogen and phosphorous.

Lead author Dr Paul Carnell, from RMIT University’s Centre for Nature Positive Solutions, said the findings could be applied more broadly across Australian coastal waters.

“It seems insurmountable, and that’s something that I think has been holding us back a little bit with urchins – like, where do you start? And what we really saw was if you look at the costs and benefits … there’s a clear path forward.”

Marine ecologist Scott Bennett from University of Tasmania, a co-founder of the Great Southern Reef Foundation, said practiced divers could collect a tonne of long-spined urchins in about three hours.

“Its numbers have increased in southern NSW, but certainly down here in Tasmania, the population has just gone through the roof,” Bennett said. “And that’s climate related. So it’s the warming ocean currents and strengthening of the East Australian Current, facilitated by climate change.”

He saw long-spined urchins as an unlikely source of climate change-related hope.

Urchin roe is considered a delicacy in parts of Asia and can retail for $275 for 100 grams of high-end product. Bennett said the most ecologically effective form of harvesting was at the edges of kelp forests that had not yet been denuded by urchins.

“This is a climate-related impact, but it’s one that does have really tangible and genuine solutions, and those solutions are meaningful – they can have hugely positive benefits for the reef,” Bennett said.

“But at the same time, the urchin industry is a little bit on a knife edge in a sense. It could explode and become a big, really lucrative industry and sustainable fishing industry, which, in today’s world is an oxymoron … but it could also just fall in a heap because it does need that incentive behind it.”

A taskforce set up to tackle the problem of long-spined sea urchins recommended a $55 million federal government investment into research, monitoring and targeted culls, which was endorsed by a 2023 Senate inquiry into urchins.

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A spokesperson for the Department of Climate Change, Energy, the Environment and Water said the federal government was considering its response to the Senate inquiry into climate-related marine invasive species.

“The inquiry’s recommendations regarding national co-ordination and investment into long-spined sea urchin control and establishing a viable fishery are being carefully considered, noting the issues are complex and require co-ordinated management responses across multiple jurisdictions.”

The Invasive Species Council is not in favour of subsidised commercial harvesting of urchins, arguing it could create perverse outcomes including industry opposition to more effective long-term urchin control strategies.

Co-founder Tim Low said it would be better for government agencies to conduct control works rather than trying to subsidise industry.

Greens senator Peter Whish-Wilson, who chaired the 2023 Senate inquiry into long-spined sea urchins, said some of the barrens stretched kilometres, with barren rock covered in urchins.

“Where’s the best bang for our buck in terms of spending money on tackling this issue and developing the fishery? The answer is actually incipient barrens [areas where urchins are beginning to overgraze] because that’s where the urchins have the best quality [roe], and you can get the best biodiversity and habitat protection because you’re stopping new barrens being formed in areas of high biodiversity.”