Crown-of-thorns starfish alert

Crown-of-thorns infestation, GBR. New evidence points to a link between outbreaks of the starfish and water quality. Image: AIMS Long-term Monitoring Team.

Population outbreaks of the coral-eating Crown-of-thorns starfish Acanthaster planci , continue to kill more coral on Indo-Pacific coral reefs than other disturbances, but the causes of these outbreaks have not been resolved.

AIMS conducted experiments where larvae were reared on natural phytoplankton.We also examined long-term data of river floods, chlorophyll concentrations and starfish outbreaks on the GBR. Computer simulations investigated the relationship between the frequency of outbreaks and larval food availability.

The experiments showed that the odds of A. planci larvae completing development increases ~8-fold with every doubling of chlorophyll concentrations up to 3 µg L-1.

Field data and the population model showed that river floods and regional differences in phytoplankton availability are strongly related to spatial and temporal patterns inA. plancioutbreaks on the GBR. The model showed that, given plausible historic increases in river nutrient loads over the last 200 years, the frequency ofA. planci outbreaks on the GBR has likely increased from one in 50 – 80 years to one every 15 years, and that current coral cover of reefs in the central GBR may be 30 – 40% of its potential value. This study adds new and strong empirical support to the hypothesis that primaryA. plancioutbreaks are predominantly controlled by phytoplankton availability, strongly supporting proposed reductions in terrestrial runoff through the Government's Reef Rescue initiative.