Crown-O-Thorns starfish

Crown-of-thorns starfish eradication on Rarotonga

You got to to love the diving in Rarotonga! Great visibility and warm water combined with our fascinating marine life makes scuba diving in Rarotonga extremely fun and explains why many divers keep coming back year after year.

Crown-of-thorns starfish suckers and spines
Crown-of-thorns are beautiful starfish

Amongst our natural reef inhabitants are the beautiful Crown-of-thorns starfish, aka COTS and locally known as taramea.
COTS are natural reef predators and have evolved over millions of years. These starfish have thousands of suckers and venomous spines. Crown-of-thorns starfish are feeding on coral and are important for the natural growth and health of the coral reefs. Their preferred food are fast growing corals. By primarily feeding on fast growing corals they make space for the slower growing, reef building corals, which in turn is important for the healthy growing of the coral reef.

Crown-of-thorns starfish feeding on coral
Crown-of-thorns starfish feeding on coral

As long as crown-of-thorns numbers stay within normal, sustainable limits, these starfish have an important role to keep coral reefs healthy. Problems start when the COTS reproduce too fast. In great numbers, crown-of-thorns starfish can become highly destructive to coral reefs. The reasons for faster than usual reproduction rates are not fully understood, but it is believed that factors like high nutrient levels, climate change and lack of natural predators can contribute to fast reproduction rates.

Crown-of-thorns starfish in containers on boat
Removed COTS are taken to land

Rarotonga ‘s reefs are stunning with beautiful hard coral formations. During the last months, higher than usual COTS numbers have appeared on Rarotonga’s reefs, mainly on the north and north-west coasts of the island. To help keep our reefs healthy and to control the COTS population to prevent an outbreak, we have been helping alongside NGO Kōrero O Te ‘Ōrau and Ministry of Marine Resources Cook Islands with the scoping and removal or culling of COTS.

Crown-of-thorns starfish laying on grass
COTS serve as fertilizer for local growers

After being removed from the water, the starfish are being used as fertilizers by local growers.

Attempts have also been made by a small number of locals to eat the roe in an attempt to get more value out of the removed starfish, however to this day the number of crown-of-thorns starfish roe disciples is still very small.

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