Divers in the Cook Islands, a small South Pacific nation, are plunging wooden spears into mobs of starfish. It’s for good reason—these creatures have turned already sensitive tropical coral reefs into all-you-can-eat buffets.
While crown-of-thorns starfish are native to the Indo-Pacific region, massive outbreaks of them across their range have descended upon reefs around the world over the past few decades. This is likely worsened by human activities such as overfishing the echinoderm’s natural predators and farming with heavy fertilizer application and subsequent runoff. As an adult, one of these starfish—called taramea in Cook Islands Māori—can chomp through more than 100 square feet of reef annually. They consume coral by shoving their stomachs out of their mouths, coating the reef with digestive enzymes, and slurping up nutrients.
After past attacks from these starfish, reefs have taken decades to recover. Now, climate change-induced coral bleaching and ocean acidification could make it tricky for South Pacific coral reefs to bounce back. Scientists have employed the assistance of poison-injecting robots to defend the Great Barrier Reef, and some researchers are developing traps that lure in the spiny animals with chemicals—they apparently have a strong sense of smell. But many of these efforts are still in the experimental stage.
For a quicker solution, divers in the Cook Islands are going the manual route: stabbing crown-of-thorns starfish with hooked sticks and collecting them on boats, AFP recently reported. The environmental group Kōrero O Te 'Ōrau, translated from Cook Islands Māori as Knowledge of the Land, Sky, and Sea, enlists the help of volunteer divers and clears away thousands of these starfish each year. But these menaces don’t go to waste: Some serve as garden fertilizer once they reach land. 
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