Coral bleaching and the Proliferation Of Crown-Of-Thorns Starfish

Global warming has many side-effects, one of which is the exacerbation of coral bleaching. Another side-effect is the proliferation of crown-of-thorns starfish, which are resistant to marine heatwaves and devour coral reefs.


The crown-of-thorns starfish (frequently abbreviated to COTS), Acanthaster planci, is a large starfish that preys upon hard, or stony, coral polyps (Scleractinia). The crown-of-thorns starfish receives its name from venomous thorn-like spines that cover its upper surface, resembling the biblical crown of thorns. It is one of the largest starfish in the world.

New information about the crown-of-thorns starfish has come from research led by Professor Maria Byrne from the School of Life and Environmental Sciences at the University of Sydney and published in the journal Global Change Biology. Byrne and colleagues found that juvenile crown-of-thorns starfish had a higher heat tolerance than not only coral, but also adults of the same species.

It has been found that juvenile crown of thorns starfish can tolerate almost three times the heat intensity that causes coral bleaching. This heat tolerance, combined with the life cycle of the crown of thorns starfish makes it uniquely able to prey on vulnerable coral. The juvenile starfish are herbivorous and can therefore survive not only the temperatures that cause a bleaching event, but also the resulting lack in coral to feed on. In fact, the deteriorating coral gives the juvenile starfish a “rubble habitat,” that allows their numbers to build over time, according to Byrne. When the reef finally begins to regrow, the juveniles emerge fully grown carnivores and eat the new coral. Previous research from Byrne suggests that the juveniles can wait for up to six years to grow into coral-eating adults. The resiliency, life cycle, and adaptability of the crown-of-thorns starfish add up to an organism that is uniquely suited to destroying coral reefs.

Loss of natural predators due to overfishing and the buildup of nutrients in the water have also contributed to outbreaks of crown-of-thorns starfish.