Cook Islands battles hungry starfish invasion

The Fight Against Crown-of-Thorns Starfish in the Cook Islands

Divers, armed with wooden spears, dive deep beneath the ocean’s surface, engaging in a critical battle against a growing threat to coral reefs. These divers are on a mission to combat the crown-of-thorns starfish, a species that is rapidly destroying the delicate ecosystems of the Cook Islands.

These creatures, known for their venomous spikes and insatiable appetite for coral, have become a major concern for marine biologists and environmentalists. The Cook Islands, a small nation in the South Pacific, has been experiencing an outbreak of these starfish for years, according to marine biologist Teina Rongo. He explains that the impact can be devastating, potentially wiping out entire reef systems around the islands.

Rongo, who leads volunteer efforts to protect the reefs near Rarotonga, notes that this issue is not isolated to the Cook Islands. “We’re hearing about similar challenges in other countries across the Pacific,” he says. This suggests a broader regional problem that requires coordinated action.

Each adult crown-of-thorns starfish can consume over 10 square meters of coral annually. They use their unique anatomy to wrap their stomachs around the coral, digesting it from the inside out. This feeding behavior poses a serious threat to coral reefs, especially those already weakened by climate change.

In Australia, scientists are exploring innovative solutions to tackle the crown-of-thorns starfish. Some researchers have developed robots designed to hunt and inject these starfish with poison. According to Sven Uthicke, a researcher at the Australian Institute of Marine Science, the injection method can use various substances such as vinegar or lime juice. Other teams are experimenting with chemical traps, though these methods are still in development.

For Rongo, the most effective tool remains a simple wooden stick made from the dense timber of the Pacific Ironwood tree. The stick, equipped with a hook, allows him to pry the starfish off the coral without getting injured. However, the process is not without its challenges, as the starfish can cause painful pricks.

Crown-of-thorns starfish are named for their numerous venomous spikes and can grow to the size of a car tire. Normally, they exist in low numbers and do not pose a significant threat. However, when their populations explode, they can strip entire reefs of life in a short period.

The Australian Institute of Marine Science describes the spawning of these starfish as occurring in "plague proportions," highlighting their role in the decline of coral reefs. From the Red Sea to the Pacific Ocean, these outbreaks are becoming more frequent and severe.

Experts believe that factors such as nutrient runoff from agriculture and changes in predator populations may contribute to these outbreaks. However, the damage is exacerbated by the weakening of reefs due to climate change, including coral bleaching and ocean acidification.

Rongo emphasizes the importance of protecting the reefs, stating, “This is why it's important for us to help the reef.” Divers search the reefs for hard-to-spot starfish, often hidden in dark crevices. Once found, the starfish are removed and pierced with thick rope to be transported back to the boat.

After a day of work, the collected starfish are placed in a plastic chest and taken ashore for counting, measuring, and eventually being turned into garden fertilizer. In the local language, these creatures are called “taramea,” which translates to “spiky thing.”

Volunteers working with Rongo and his environmental group, Korero O Te Orau, remove thousands of starfish each year. Rongo is motivated by the devastation caused by a previous infestation in the 1990s. “I was part of that eradication effort,” he recalls. “We were too late when we decided to act. It went on and ended up killing the reef.”