Crown of thorns starfish (COTS) remain one of the major stressors on the Great Barrier Reef. The COTS control programs have been running for years, the methodology has evolved, and the 2026 picture is genuinely more sophisticated than the equivalent 2020 picture. The honest read on whether it’s working is mixed.

The fundamentals of the problem haven’t changed. COTS are native to the Reef. Their populations cycle naturally. The current concern isn’t their existence but the frequency and intensity of outbreak events, which appear linked to nutrient enrichment from terrestrial runoff and to changes in predator populations. When COTS are at high density, they consume coral faster than the reef can recover, and a single outbreak can do significant damage to a region of reef.

The control approach has consolidated around vessel-based culling teams using injection methods that kill individual starfish without harming surrounding reef. The current method — single-injection of bile salts — works reliably and is much faster than the older multi-injection methods. Trained divers can cull substantial numbers of starfish per hour when COTS density is high.

The vessel program operates across multiple platforms working different sections of reef. The COTS Control Program coordinated through the Great Barrier Reef Marine Park Authority and partner organisations covers priority reefs across the World Heritage Area. The deployment pattern is data-driven: surveying for COTS density, prioritising reefs with both high COTS pressure and high coral value, and targeting the culling effort there.

What’s genuinely working in 2026: the surveillance side has improved dramatically. The combination of dive surveys, sled-tow surveys, drone-based aerial surveillance for shallow areas, and increasingly some autonomous underwater surveying produces a picture of COTS distribution that the program can act on faster than in earlier years. The reaction time from outbreak detection to deployed culling teams has compressed.

What’s still hard: the underlying drivers. COTS outbreaks are believed to start with terrestrial nutrient pulses that enable larval survival at higher rates than baseline. The terrestrial nutrient story — fertiliser runoff from sugarcane, banana, and other Queensland coastal agriculture — is being addressed through the Reef 2050 plan and a series of regional water quality programs. The progress is real but slow. The agricultural water quality conversation has been ongoing for two decades, and meaningful improvement requires sustained policy and farm-management change that operates on agricultural rather than ecological timescales.

The reef recovery picture in areas where COTS have been controlled is encouraging. Reefs that received sustained control attention through the past decade have generally maintained better coral cover than equivalent uncontrolled reefs. The before-and-after data on specific reefs supports the case that the control program is doing real work, not just maintaining the appearance of intervention.

The bleaching and climate change context complicates the COTS conversation. A reef under thermal stress is less able to recover from COTS predation. A reef that’s already been damaged by bleaching is more vulnerable to a subsequent COTS outbreak. The interaction between climate stressors and biological stressors is non-linear, and the 2026 reef science emphasises this interaction more carefully than earlier framings did.

The genetic and biological control research continues. Various research programs have explored whether COTS pheromone-based aggregation, biological control through natural predators, or genetic intervention might offer additional management tools. The honest read in 2026 is that these are research-stage rather than operational. The bile-salt injection method remains the workhorse and is likely to remain so for several more years.

The funding question is real. The COTS control program is expensive. The case for sustained funding rests on the marginal value of preventing coral loss in priority reefs, which is genuinely meaningful but politically vulnerable when budgets tighten. The 2026 funding position has held up reasonably well, but the program’s continued effectiveness depends on continued investment.

The community engagement and citizen science components of the broader Reef monitoring effort have expanded. Several programs train recreational divers to contribute to COTS surveillance, increasing the surveillance footprint at relatively low cost. The data quality from trained citizen divers is high enough to feed into the formal control program planning, which is a credit to the program design.

For Australians who care about the reef, the COTS control story is one of the few clear cases where direct ongoing intervention demonstrably reduces a stressor on the system. It’s not a complete solution. The reef faces existential pressure from climate change that COTS control can’t address. But the COTS work is real conservation that produces measurable benefit, and it deserves the funding and attention it gets.

The longer-term direction is for the COTS program to continue while the broader systemic interventions — water quality, climate action, reef restoration research — develop on their longer timescales. The COTS control buys time for the bigger interventions to take effect. That’s a sensible role for it to play.