Efforts are underway in the Cook Islands to eradicate the crown-of-thorns starfish, which has re-appeared on the reef around Rarotonga.
The crown-of-thorns feed on hard coral, and the reef had been devastated by the pest in the past.
The head of the environmental NGO Korero o te Orau, Teina Rongo, said members have discovered the beginnings of an infestation.
He said they had begun removing the pest, but they might need government help.
"What we have seen from the past is the recovery is getting slower and slower and slower. So the concern is, because we have the impacts of climate change contributing to problem of the recovery. So our concern is that if this reef dies again, as a result of crown-of-thorns there is no guarantee that it will come back, or if it does, it will probably take much longer than the previous recovery," he said.