Crown-of-thorns removal mission!

A Crown-of-Thorns starfish (Acanthaster planci)
The crown-of-thorns (Acanthaster planci), is a large, thorned starfish which lives along the shallow reefs of the tropical band of the globe. It has all the fundamental components of any other starfish - a central disk, perimeter by radiating arms - but unlike most, this starfish can have up to 23, regenerative arms (all of which can be replaced in the case of lost limbs) covered with long poisonous spines. Usually found ranging between 25 cm – 35 cm in its adult stage, some individuals can be as large as 80 cm. The crown-of-thorns is a carnivorous predator, feeding on live coral tissue by everting its stomach over their surfaces. As well as hard corals, they can also feed on soft corals, sponges and encrusting organisms. Their presence on a reef give slower growing coral communities (e.g. Favites) an opportunity to flourish by preferring feeding on branching and plate fast growing corals (e.g. Acropora) However, the large size of the starfish and its propensity of spectacular population outbreaks can result in massive coral mortality. The Seychelles experienced their last outbreak in 2014 on the Northwest coast of Mahé.  The main hypothesis for population outbreaks are nutrient enrichment that might increase the availability of food source for the larvae and the removal of their natural predators such as the triton shell (Charonia tritonis), some Pufferfish (Tetraodontidae), Triggerfish (Balistidae) as the Titan Triggerfish (Balistoides viridescens) and the humbhead wrasse (Cheilinus undulatus).

A starfish arm covered with long poisonous spines



Some of the collected crown-of-thorns
Following major disturbances such as a bleaching event, reefs are in the process of recovery. The heavy presence of those voracious predators might negatively affect the reef recovery trajectory as they feed on the newly settled coral colonies. The Fisherman’s Cove reef is under both global threats, resulting from the climate change such as increasing sea water temperatures leading to coral bleaching, and local threats such as physical human damages.
To promote the natural recruitment and hence the recovery of the Fisherman’s Cove reef, the MCSS Coral Cove team has decided to remove the excess of crown-of-thorns starfish from the reef. Eighteen individuals were taken out from the reef the same day in just two trips along the snorkelling trail. The team will keep watching the reef for any overabundance of these coral predators.





Watch the video of our Crown-of-thorns removal mission by Carolyn Cowan, one of volunteer!


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