Crown-of-thorns starfish (Acanthaster planci) or COTS are major predator of corals throughout the tropical Indo-Pacific region. Their appetite for coral flesh is enormous with individual adult starfish consuming up to 10 m2 of live coral tissue per year.
COTS exhibit population explosions, and can be a major cause for coral loss on reefs, as has been documented on the Great Barrier Reef (GBR). Corals cannot withstand the onslaught of feeding COTS during an outbreak.
AIMS is engaged in research to understand the causes of COTS population explosions and to develop new methods to control outbreaks. The Institute also actively monitors changes in COTS populations along the GBR through its Long-Term Monitoring Program.
Experimental studies on COTS larvae
One of the leading hypotheses to explain the occurrence of COTS outbreaks comes from laboratory studies in which substantially more planktonic COTS larvae survived to settle onto the coral when their phytoplankton food was present at high concentrations .
On the GBR, higher concentrations of phytoplankton are often found in flood waters, as a result of increased nutrient runoff.
Historical flood records, COTS monitoring data and models suggest that increased survivorship of larval COTS following floods leads to primary outbreaks of COTS in the northern regions of the GBR. These many adults associated with primary outbreaks spawn immense numbers of larvae that are transported southward down the GBR by ocean currents. After larval settlement, the new starfish also grow and spawn, leading to outbreaks on reefs further to the south.
Using the National Sea Simulator (SeaSim), researchers will study the response of COTS larvae and their survivorship under different nutrient, salinity, carbon dioxide and temperature regimes to establish links between population outbreaks and the availability of nutrients in the water and to understand the effects of a warming and more acidic ocean on COTS populations.
Better ways to control COTS populations
The decline in coral cover on the GBR shows that COTS are a major threat to the long term viability of coral reefs. There is an international consensus that research is required to find new effective, safe and socially acceptable methods of widespread control using novel approaches.
AIMS has received support from the Australian Government ‘Caring for Country' initiative through its Reef Rescue program to fill critical knowledge gaps to identify COTS vulnerabilities to address this need.
Researchers are investigating the ability of COTS to respond to chemical signals in the marine environment and to exploit behavioural traits to develop an effective control management technology.
AIMS has surveyed COTS populations on the GBR since 1983 as part of its Long-Term Monitoring Program. Spanning 30 years, the program also collects information on coral cover, incidences of coral bleaching and coral diseases, and is the longest and most comprehensive data set on the health of the GBR. The Long-term monitoring program makes an important contribution to the Great Barrier Reef Outlook Report, the Australian Government's five-yearly assessment of the state of the GBR.
Current and historical information on COTS populations on the GBR can be found online.