While our reefs are subject to human threats on an almost daily basis in most places, they are also under threat by some natural competitors, diseases, and predators, all of which seem to have been made worse by humanity’s actions as a whole. One of the biggest threats to healthy reefs is the crown of thorns starfish, a spiny, toxic animal that feeds on living coral polyps.
Why the Crown of Thorns Starfish is a Threat
Before overfishing and global warming was a problem, crown of thorn starfish posed little, if any threat to marine environments. Today, their population is exploding.
Large, nocturnal sea stars that prey upon living coral, these solitary animals are endemic to tropical coral reefs throughout the Pacific Ocean, the Indian Ocean, and the Red Sea. The second largest of all the world’s sea star species, surpassed in size only by the harmless sunflower starfish, the crown of thorns starfish gets its name from the thorny looking venomous spikes that cover its body, giving it as much appeal as an underwater cactus might have. Capable of piercing wetsuits and injuring divers, these starfish release chemicals when they feed, which attract additional crown of thorns stars to healthy reef sections, where they begin their destructive feeding frenzies, extruding their stomachs, which contain digestive enzymes, onto the reef, liquefying the coral tissue.
A single crown of thorns starfish can consume as much as six square meters of living reef annually; and, as they have only a few natural predators, they continue to breed and thrive, especially in areas where predators such as humphead wrasse and other large reef fish capable of taking on full grown specimens have had their populations decimated by overfishing.
What Can Be Done to Slow or Halt Crown of Thorns Starfish Invasions
Now, it is up to humanity to work to save reefs from crown of thorns starfish invasions. It all begins with ending overfishing, and bringing marine life numbers back up to where they were prior to the days when commercial fishing operations began in earnest. This is due to the fact that crown of thorn stars begin their lives as plankton; being fed upon by whales and other filter feeders. As they grow, they are subject to predation by fish and other animals that consume smaller organisms.
Until predatory species are brought back to health, people have begun attacking the starfish themselves, sometimes hacking them to bits with dive knives (not a good strategy, as they are capable of regenerating), and sometimes burying them beneath heaps of rubble, which is still not the best solution, since they can live for months without food and are still capable of reproducing.
One of the newest, most promising techniques for killing off crown of thorns starfish is to inject them with a solution of sodium bisulphate, which kills the sea star, but does not harm the coral reef.
Like other animals that have caused problems when populations explode, crown of thorns starfish do have a place in the environment; in fact, in a healthy environment, they prevent the fastest growing corals to take over slower growing species, keeping biodiversity high and enriching the environment. Until reefs and other animals are brought back to a state of health however, population control is a must. If they’re a problem where you dive, look into volunteering with a control team. By sharing just a little of your time, you really can make a big difference.