What drives crown-of-thorns starfish outbreaks?
Runoff and deep-sea upwelling combine on reefs
Research summarized in the newest Great Barrier Reef coverage points to a “perfect storm” mechanism behind crown-of-thorns starfish (COTS) outbreaks: conditions driven both from land and from the deep ocean.
The key idea is that upwelling from deeper waters can change the near-surface environment where COTS feed and where early life stages develop. At the same time, runoff from the land can alter local water quality and nutrient levels entering the reef system. When these two drivers occur together, the reef may become more favorable for COTS to boom.
Why this matters
COTS outbreaks are a major cause of reef degradation because they can rapidly consume live coral. If warming and circulation changes increase how often upwelling and runoff align, managers may face outbreaks that are harder to predict and harder to prevent with only local interventions.
What to watch next
The coverage frames the problem as multi-source and multi-process rather than a single stressor. That implies:
- Waters near the reef may need monitoring not just for temperature, but also for signs of upwelling influence.
- Land-based inputs (through agricultural and urban runoff patterns) may be linked to outbreak timing.
- Coordination of datasets across catchments and oceanographic measurements could improve seasonal risk forecasting.
Overall, the hypothesis shifts outbreak thinking toward an interacting system—where the reef’s condition depends on both ocean physics and the chemistry delivered from land.