Restoring Port Phillip Bay's dwindling kelp forests by culling overgrazing sea urchins would deliver more than $92 million in benefits, a new study has found.
Kelp provides shelter and food for countless species while removing pollutants like nitrogen and phosphorous from the water, but native sea urchins that feed on the kelp have reached unsustainable population levels.
Now for the first time, the return on investment of targeted sea urchin culling and kelp restoration in Victoria's Port Phillip Bay has been calculated.
In a study led by RMIT University, new economic modelling shows the best return-on-investment scenario comes from a $50 million investment in targeted culling and kelp restoration, which would return up to $92 million in economic benefits.
Lead author of the study, Dr Paul Carnell, said although climate change and human factors were also to blame for disappearing kelp forests, managing overabundant sea urchin populations is key to restoring healthy reefs.
"Managing the bay's sea urchin population is a practical step we can take to ensure the health of Port Phillip Bay, which is 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.
"This approach can be targeted to specific areas of the bay, so we can get the greatest bang for our buck."
For the study, published in Ecosystem Services, researchers modelled the costs and benefits of urchin culling at different sites in Port Phillip Bay, factoring in urchin density, dive depth, travel time and the potential for kelp to boost nitrogen storage.
The $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 $92 million gained would be from the value of removing nitrogen from the 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 restore these reefs," he said.
The research was led by RMIT with Deakin University, The University of Melbourne, University of Western Australia, and Canopy Economics and Policy. It was funded by the Victorian Government Department of Environment, Land Water and Planning.
'Prioritising investment in kelp forest restoration: A spatially explicit benefit-cost analysis in southern Australia' is published in Ecosystem Services. DOI: 10.1016/j.ecoser.2025.101739.
