Researchers from the University of Tasmania have successfully restored kelp forests along Tasmania’s east coast by removing sea urchins that had created expansive marine “barrens” devoid of seaweed and associated marine life.

The project targeted 50 hectares of rocky reef that were overgrazed by long-spined sea urchins, a species that has expanded its range southward as waters warm. By removing about 80% of urchins, researchers triggered rapid kelp recovery, with dense kelp forests re-establishing within 12-18 months.

Professor Craig Johnson, who leads UTAS’s Institute for Marine and Antarctic Studies, said the restoration demonstrates that ecosystem shifts driven by climate change aren’t necessarily irreversible. “The urchin barrens appeared to be a stable alternative state, but removing the grazing pressure allowed kelp to recolonise quickly from nearby healthy reefs.”

Long-spined sea urchins normally occur in New South Wales waters but have been extending their range into Tasmania as the East Australian Current strengthens and brings warmer water south. The urchins have few natural predators in Tasmania and can overgraze kelp forests, creating barren areas where coralline algae and bare rock dominate.

These barrens support much less biodiversity than kelp forests. Fish, abalone, rock lobsters, and other commercial species depend on kelp forests for food and habitat. Losing kelp has economic impacts beyond ecological damage.

The restoration involved teams of divers methodically removing urchins using hand tools. It’s labour-intensive work, with divers collecting 50,000-100,000 urchins per hectare. The collected urchins are processed for fertiliser or animal feed, partially offsetting collection costs.

Initial trials tested whether urchin removal was sufficient for kelp recovery or whether active kelp planting was necessary. Fortunately, kelp spores present in the water and surviving microscopic kelp stages in the barrens were sufficient for recovery once grazing pressure was removed.

That’s important because kelp planting is even more labour-intensive than urchin removal. It involves growing kelp in hatcheries, attaching juvenile plants to substrate, and deploying them underwater. That approach works but costs substantially more.

The restoration sites have been monitored quarterly since urchin removal. Kelp recovered rapidly in most areas, reaching canopy cover comparable to healthy reference sites within two years. Some areas recovered more slowly, apparently because residual urchins that escaped initial collection continued grazing.

Maintaining restored kelp forests requires ongoing urchin control. Juvenile urchins continue recruiting to reefs from offshore populations, and if they’re allowed to reach high densities again, they’ll overgraze the restored kelp.

The research team estimates that follow-up urchin removal every 2-3 years is sufficient to maintain kelp forests. That’s much less intensive than initial restoration but still requires ongoing effort and funding.

One question is who should pay for urchin control. The restoration provides public benefits through improved ecosystem function and supports commercial fisheries. But it’s not clear whether government agencies, fishing industry groups, or some combination should fund ongoing management.

Tasmania’s recreational fishing groups have shown interest in supporting restoration because kelp forests enhance fish habitat. Some rock lobster fishers support it because lobsters are more abundant in kelp forests. But abalone fishers are ambivalent because urchins and abalone compete, and removing urchins might actually increase abalone predation by rock lobsters.

These competing interests complicate governance of restoration programs. Finding funding models that align incentives remains challenging.

The UTAS research has attracted international attention. Urchin barrens affect coastlines worldwide, from California to Norway to Japan. Tasmania’s restoration success suggests that active management can reverse ecosystem degradation even when climate change is driving ecological shifts.

However, critics point out that urchin removal addresses symptoms rather than causes. The underlying problem is warming waters that allow urchins to thrive in new areas. Unless climate change is addressed, urchin range expansion will continue, requiring ever-larger restoration efforts.

That’s true, but researchers argue that restoration still provides benefits. Even if restored kelp forests need ongoing maintenance, they provide ecosystem services and fisheries support that would be lost if barrens were left unmanaged.

Economic analysis suggests restoration costs about $15,000-20,000 per hectare for initial urchin removal, with follow-up treatments costing $3,000-5,000 per hectare every few years. Whether that’s worthwhile depends on how you value ecosystem services and fisheries benefits.

Some commercial dive operators have incorporated urchin removal into their business models, offering “eco-tourism” where recreational divers participate in restoration while paying for dive trips. This helps fund restoration while engaging the public in marine conservation.

The collected urchins present an opportunity if markets for urchin products can be developed. Sea urchin roe is a delicacy in some markets, but the long-spined species has poorer quality roe than species commercially harvested elsewhere. Alternative uses as fertiliser or aquaculture feed are being explored.

The UTAS restoration project is now scaling up to cover several hundred hectares along Tasmania’s east coast. That represents only a small fraction of urchin barren extent, which totals thousands of hectares, but focuses on areas with high biodiversity or fisheries value.

Whether restoration can be scaled to address barrens at coastline-wide scales depends on developing more cost-effective control methods. Researchers are testing automated urchin collection using remotely operated vehicles, biological control using urchin predators, and selective urchin culling that leaves some urchins but prevents densities from reaching overgrazing thresholds.

None of these approaches are ready for commercial deployment yet, but they represent promising research directions that could reduce restoration costs substantially.

The Tasmanian kelp restoration project is part of broader efforts to understand and manage climate-driven marine ecosystem changes. UTAS is also studying range shifts of other species, adaptation of commercial fish stocks to warming waters, and implications for marine park management.

Whether restoration can keep pace with climate change impacts remains uncertain. But the Tasmanian experience demonstrates that active management can restore degraded ecosystems and buy time while longer-term climate solutions are developed.