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Restoring underwater kelp forests by culling overgrazing sea urchins would deliver significant financial benefits, a new study has found.

Kelp provides shelter and food for countless species while removing pollutants like nitrogen and phosphorus from the water. But sea urchins that feed on the kelp have reached unsustainable population levels in southern Australia.

In a new study led by RMIT University, researchers found that despite the cost, restoring southern Australian reefs from urchin barrens is feasible and beneficial for improved water quality, fisheries and carbon sequestration.

The study's lead author, Dr. Paul Carnell, said although climate change and human factors were also to blame for disappearing kelp forests, managing overabundant sea urchin populations was key to restoring healthy reefs.

"Managing the sea urchin population is a practical step we can take to ensure the health of our waterways, which are crucial to local ecosystems, tourism and food security," said Carnell, a senior lecturer at RMIT's Centre for Nature Positive Solutions.

"Now we have the figures to show this is also a smart economic investment."

Australia's kelp forests have been declining, with kelp cover in Victoria's Port Phillip Bay , while the native purple sea urchin has become 2.5–4.2 times more abundant.

For the study, published in , researchers modeled the costs and benefits of urchin culling at different sites in Port Phillip Bay, factoring in urchin density, dive depth, travel time and kelp's potential to boost nitrogen storage.

Economic modeling showed an AU$50 million investment in targeted culling and kelp restoration would return up to AU$92 million in economic benefits.

The AU$50 million investment would go towards paying commercial divers to cull sea urchins and the cultivation and deployment of kelp to help restore reefs, creating jobs in those sectors.

Most of the AU$92 million gained would be from the value of removing nitrogen from Port Phillip Bay, but also includes boosts to recreational fishing and carbon storage to mitigate climate change, Carnell said.

"We know from previous trials in Port Phillip Bay that this is an effective approach to restoring these reefs," he said.

The researchers hope this study will guide the future prioritization of kelp restoration on reefs that have degraded through sea urchin overgrazing.

The research was led by RMIT with Deakin University, The University of Melbourne, University of Western Australia, and Canopy Economics and Policy.