Destructive starfish is delicious to some

Crown-of-thorns starfish, the scourge of Australia’s Great Barrier Reef, may have more natural predators than we thought.

A novel study of fish faeces and gut contents suggests a number of fish are interested in Acanthaster solaris, including popular eating and aquarium species.

The native starfish has surged to plague proportions three times since 1962, with a fourth under way. Each time it has caused a significant loss of large amounts of hard coral. 

Increasing the amount of predation has long been touted as a potential solution to preventing outbreaks but, aside from a mollusc called the Giant Triton (Charonia tritonis), identifying what eats it has proved challenging.

Now a team of scientists led by Frederieke Kroon from the Australian Institute of Marine Science has applied a genetic marker unique for crown-of-thorns, developed at AIMS, to detect the presence of starfish DNA in fish faeces and gut contents.

Researcher Frederieke Kroon examining a crown-of-thorns starfish. Credit: D Westcott/CSIRO

Over three years, they used it on samples taken from 678 fish from 101 species, comprising 21 families, gathered from reefs experiencing varying levels of starfish outbreak.

The results, published in the journal Scientific Reports, confirm that at least 18 coral reef fish species – including Spangled Emperor (Lethrinus nebulosus), Redthroat Emperor (Lethrinus miniatus) and Blackspotted Puffer (Arothron nigropunctatus) – eat young or adult starfish.

Significantly, nine had not been previously been reported as doing so, including the Neon Damsel (Pomacentrus coelistis), Redspot Emperor (Lethrinus lentjan), and Blackspot Snapper (Lutjanus fulviflama).

“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,” says Kroon, who worked with colleagues from AIMS, the CSIRO and the Great Barrier Reef Marine Park Authority.

New management approaches to mitigate crown-of-thorns outbreaks by enhancing coral reef fish predation should be seriously considered, the researchers write, “both on the GBR and on Indo-Pacific reefs more broadly”.

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