Skip to main content

Crown of Thorns Removal - Mango Bay 31st July 2014


Sunshine Divers and Bans Diving Resort Divemasters in Training and those interested joined in on a project to remove the Crown of Thorns that had accumulated in Mango Bay.

The Day began with a Francois (marine biologist) giving us some information about the Crown of Thorns and how we need to be aware with collecting these creatures to avoid any injuries.

We collected in total 7 Crown of Thorns starfish, of various sizes. When we collected them we took down specific information to help with finding out the reasons for why they are there.

Data collected included the Depth of the crown of thorns, where was it located being on coral or sand, and the dimensions of the diametre of the starfish.

Here are just a few comments from the Divemasters who participated in this eco program and how what they felt about their experience:

"Great First experience about working underwater" - Sara

"Star Wars " - Flo

"Dirty Job but someone has to do it!" - Louis

"Different way of diving, having an actual task and seeing it through is an awesome experience. Communication and a good detailed briefing is essential" - Francois

"Teaches you alot according to team work and what to consider if you plan a program such as this one, I enjoyed combining my diving with a cause! Was Cool ! - Jenny

"Great Dive with a more environmental element, I had a really good time and learned alot" - Denise

"First one very good eco experience" - Alex

"Really enjoyed participating in searching and removing these starfish" - Sander

"It was a very long swim to and from the boat" - Chloe


INFORMATION ABOUT THE  CROWN OF THORNS    The Crown-of-Thorns starfish (Acanthaster planci) feeds on coral. Low numbers of this starfish increase reef diversity, but large numbers can destroy reefs. Avoiding human activities that increase starfish numbers is more effective than trying to control Crown-of-Thorns outbreaks once they happen.   The Crown-of-Thorns starfish is a predator of coral. In low densities, this starfish promotes diversity in coral reef ecosystems, because it prefers to feed on fast growing Acropoid coral. This gives slower growing coral space to establish and grow.   Populations of the Crown-of-Thorns starfish periodically boom and when this happens thousands of starfishes swarm a reef devouring up to 90% of the coral there. This alters the coral reef ecosystem in 3 ways by: 1.lowering coral diversity and abundance 2.switching the reef ecosystem to an algae-dominated system 3.changing species composition on the reef   Crown-of-Thorns starfish outbreaks reduce diversity because many of the species that rely on coral to provide food and shelter are lost when coral is removed. Diversity loss decreases reef productivity and resilience against further disturbance.   We can make Crown-of-Thorns outbreaks worse by: •increasing nutrient levels on the reef •removing starfish predators Increasing nutrient levels on the reef 
Crown-of-Thorns starfish larvae float in the water eating plankton. Excess nutrients, from sources like fertilizer runoff and sediment, provide extra food for these immature starfish and allow more to survive to become adults.   Only a few species and reef fish can feed on the adult Crown-of-Thorns starfish because its protection of venomous spines. These predators, such as Trigger fish and the Pacific Triton, are also gathered for food or for their shells. Removing predators which help to control the Crown-of-thorns population allows starfish numbers to boom. Crown-of-thorns outbreaks happen nearly 4 times more often on reefs where fishing is allowed compared to reefs that aren’t fished.   Predators of the Crown-of-Thorns starfish change throughout its lifecycle because its defense of venomous spines becomes more formidable as it gets older. Effective biological control of the Crown-of-thorns relies on coral reef diversity because these predators change throughout the starfish’s life cycle.   Predators of Crown-of-thorns starfish larvae •sponges •bivalves •sea squirts •coral Predators of juvenile Crown-of-thorns starfish •Fireworms •Harlequin shrimp •some marine snails Predators of adult Crown-of-thorns starfish •Pufferfish •Triggerfish •Pacific Triton   Some species of crab and shrimp species defend their coral colony homes from Crown-of-Thorns attacks. These animals drive the starfish away from the coral, but do not kill them.   Our attempts to control Crown-of-Thorns outbreaks are usually unsuccessful because they are labor-intensive, ineffective over wide areas, expensive, and/or potentially dangerous. Outbreaks typically continue until disease or starvation causes starfish populations to crash.   Attempts to control the Crown-of-Thorns have included: •Cutting them up •Removing from the sea and burying them •Underwater fences •Injecting starfish with poison   Like many types of disturbance, the Crown- of-Thorns starfish can be good or bad for the coral reef ecosystem. Low numbers of this starfish increases diversity, but large numbers lower it. Our activities can add to the disturbance rate by increasing Crown-of-Thorns numbers. This erodes the sustainability of coral reefs   For the next Eco program please keep in touch and visit us on  
Action Promo Image
Take a deep dive in the complex nature of the #GlobalSharkTrade
Think shark fin soup is responsible for the decline in shark populations. Think again!

From the My Ocean Community

My Ocean is a growing community of conservation leaders. Together, our actions add up to global impact for our ocean planet.

Want to Receive Monthly Ocean News and Action Alerts?