Some of the tastiest reef fish might be in shorter supply in the future after scientists found they help protect coral by eating crown-of-thorns starfish.
Researchers have looked at decades of data on fish takes and the prevalence of the coral-eating starfish on the Great Barrier Reef.
It turns out there's a striking relationship between starfish numbers and the biomass of some fish commonly harvested for seafood.
"We found very strong relationships between the two, where the more fish you harvest, the higher crown-of-thorns starfish numbers were," says Frederieke Kroon, an ecologist with the Australian Institute of Marine Science.
"We found that for emperors, for tropical snappers, and for rockcods."
It's long been known that some fish like to eat crown-of-thorns starfish but the study led by Dr Kroon is the first to explore how fisheries harvests may affect starfish numbers.
Part of the study looked at how fish and starfish abundance differed between green-zone reefs, where fishing is banned, and blue-zone reefs where commercial and recreational fishing is allowed.
On closed reefs, the biomass of emperors, snappers and rock cods was 1.4 to 2.1 times higher and starfish densities were nearly three times lower.
"It's well known that no-take marine reserves increase fish biomass and diversity of large fishes and previous studies have suggested marine reserves could also influence starfish numbers," Dr Kroon says.
"But our study provides strong evidence there are fewer crown-of-thorns starfish on reefs with more predatory fish."
Dr Kroon says many factors are believed to contribute to outbreak proportions of crown-of-thorns starfish.
Understanding that the removal of predatory fish is one of them should help reef managers refine what they do to suppress starfish numbers. That might include altering the way fishing activities are managed.
"The next step could be to look at which reefs are particularly important in crown-of-thorns starfish outbreaks by being highly connected, spreader reefs," Dr Kroon says.
"There's already quite good information about which reefs they are.
"Then we can look at how they are managed for fisheries, and make that more targeted ... so we can basically use the fish to help us keep starfish numbers down."
The study has been published in the journal Nature Communications.
Australian Associated Press