A Starfish that Eats Coral?

By December 20, 2012Ocean Solutions

We all know about the challenges facing our coral reefs due to global climate change and anthroprogenic (human caused) effects such as overfishing, pollution and damage from divers and anchor strikes. But have you ever heard about the damage done from the Great Barrier Reef native, the Crown of Thorns Starfish? This single species has been credited with 42% of coral loss in the Great Barrier Reef in the last 27 years, second to cyclones which have caused 48%! We are going to tell you how YOU can help save reefs by stopping Crown of Thorn Outbreaks, but first…Let’s find out what they are:

What is a Crown of Thorns Starfish?


And why is it so devastating to Coral Reefs? The second largest sea star in the world, the Crown of Thorns has a large ratio of stomach surface to body mass. This large ratio has it spending about half of it’s time eating. This sea star eats coralline algae until it reaches about six months of age. After six months the sea star starts to eat hard corals and grow rapidly; up to 1m (~3 1/4 ft) in length! This sea star eats as other sea stars do, by encompassing it’s prey item (coral polyps) with it’s stomach and digesting the contents. This leaves the coral with nothing but a white skeleton, similar to the effects of coral Cotscoralbleaching (see picture on the right). Being a native species, one would think the Crown of Thorns would not do that much damage. It has always been around and so the coral must be used to it and able to recover from it’s effects, right? Right and wrong. The Crown of Thorns is only devastating to reefs when their populations are abundant and or the reef is already stressed due to climate change, a storm, and/or overfishing pressures.

What causes these outbreaks?

Factors effecting the Crown of Thorns population are still under investigation. Many scientists believe overfishing or an increase in agricultural runoff may be factors that effect the crown of thorns population. As not much is known about the larval and juvenile stages of the crown of thorns, such as its predators, it is hard to pinpoint the cause of the outbreak. It has been theorized that nutrient runoff, increasing the planktonic algal load, have always caused outbreaks, but with increasing coastal construction these nutrient loads have also increased, and so the Crown of Thorns population size.

How To Stop Outbreaks?

ocean friendly garden

If you are fortunate enough to live near the great barrier reef, show your gratitude by saying no to fertilizers, pesticides and herbicides on your lawn! Stick with native plant species and use mulch to help the plants retainer water. If you have all native plants, there should be no need to waste money on a sprinkler system, therefore reducing runoff, water usage and money! If you live on the other side of the world, no worries these practices can be put into place anywhere. Nutrient runoff is one of the main factors causing red tide outbreaks and algal blooms in any water system. The Surfrider foundations Ocean Friendly Gardens campaign encourages and helps people plant Ocean Friendly Gardens. Some of the transformations are amazing within just a year of plant growth and will create a truly unique look to your house, transforming it from just another “cookie cutter lot” into a native plant oasis.

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