Outbreaks of the crown-of-thorns starfish are a major threat to the health of reefs. The masses of starfish eat the corals and cause their destruction. One way to tackle the problem is to try to cull them, which is not an easy task. Another option is to identify the fish species that feed on the starfish and protect them to increase their numbers. Previously, fish were caught and cut open to inspect the content of their intestine to see whether they contained any crown-of-thorns starfish remains. A new, non-invasive and non-lethal approach is to collect fish poo and examine it to see whether it contains starfish DNA.