Crown-of-thorn starfish are coral-eating predators that can have more than a dozen legs and grow to 30 inches across. The starfish gets its name from the toxic thorn-like spines covering its body, which resemble a biblical “crown of thorns”.
In one year, a single starfish can eat 20 to 32 feet of coral, which can be devastating when population numbers spike. The crown-of-thorns starfish is the world’s most fertile invertebrate, with large females laying more than 200 million eggs in a season.
But scientists have noticed that while some reefs face periodic plagues of the crown-of-thorns starfish, in other areas the population is naturally kept in check. Starfish predators seemed likely. A team of researchers led by the Australian Institute of Marine Science biologist Frederieke Kroon set out to identify which fish have starfish on the menu.
The team started with a list of 71 coral reef fish from 16 families which in previous literature had been recorded feeding on crown-of-thorns. Then they caught wild fish keeping them in aquariums overnight to collect and analyze their poop for starfish DNA.
According to their paper published in the journal Scientific Reports, the fish most likely to eat settled starfish were triggerfish, groupers, humphead wrasse, spotted porcupine fish, and some Pomacanthidae angelfish. They found 18 different fish species including nine species which had never before been identified as crown-of-thorns predators.
“Just the fact that we found DNA of crown-of-thorns in fish poo to begin with was surprising to me!” Kroon tells Science News. “I thought we were looking for a needle in a haystack.”
Until now the only known predator The only well-known predator of adult crown-of-thorns starfish was the Pacific triton snail. Now, dozens of coral fish had been identified as predators of the starfishes’ sperm, very young starfish, or were observed dining on dead or almost-dead adults.
Many of the fish species found by Kroon’s team are targeted by human fishing.
“Our findings might also solve a mystery—why reef areas that are closed to commercial and recreational fishing tend to have fewer starfish than areas where fishing is allowed,” Kroon says. When human activity removes the starfish’s natural predators, their population can boom.