Tips from the Master Gardener -- Roberta Davis on eradicating the Crown of Thorns--Part 2

If you're planning a Fiji Dive trip, you'll want to read this blog by Roberta Davis who has dedicated her life to replanting coral and keeping Fiji's reefs clear of the Crown of Thorns. This is part II in the series..

Back in the good old days of a healthy, balanced ocean environment they actually served a purpose.  Their favorite meals are the faster growing branching coral species and there was generally enough of them to sustain their appetite before they would move on to the slower growing corals.   By consuming the branching corals this enabled the slower growing corals space to grow adding diversity to a reef system. Nowadays most struggling reefs  simply cannot afford an epidemic of these nasty creatures.

There are those that do not support eradicating Crown of Thorns under the premise that the outbreaks are a natural progression.  In our experience eradicating them from an area has given the returning reef at least a 5 year head start over surrounding reefs that were left to their own devices and have shown no sign of recovery in over a year.  Granted we do leave a few in the area for the Triton and its few other natural predators, but once it hits a critical mass of around 10 in an average area, it is time to cull them out.    
   
Scientists have developed ways of trying to eradicate them. Injecting sodium bisulphate into the starfish is one one of the most efficient measures in practice. Sodium bisulphate is deadly to crown-of-thorns, but it does not harm the surrounding reef and oceanic ecosystems.  Australia has spent millions of dollars on this method. Others extract the stomach acid from the Crown of Thorns and then inject it into the Crown of Thorns and their own digestive juices consume them.  Don’t ever think of chopping them up, as undoubtedly that will stress them out (which we never want to do) but they are able to regenerate from their chopped bits and pieces.

The best technique she has found is getting any water tight flotation device like a big cooler and spearing  them and getting them into the container immediately.

Having a water tight container is a key element since the crown of thorns will release their reproductive elements when they are stressed out.  (Which they are once they have been skewered). Once you have filled the container or run out of COTs, take them well above the high tide line and bury them and dump the water far away from the beach to ensure the primordial soup left in the container  will not repopulate the area again since they are extremely virile.   

Their venomous spines are not tempting to most predators but there are a few that will take on Crown of Thorns. In spite of this, the Giant Triton (a mollusk or snail and the ones that we sometimes use or call a conch which is 

blown during tiki torch lighting ceremonies). Harlequin Shrimp, Prawns, and some of the larger reef fish like the humphead wrasse  and sometimes Triggerfish (but they tend to prefer sea urchins as they are easily blown over)   Since the Crown of Thorns larvae stage is planktonic, the major control of the junior species come from planktonic predation.

We have had two Crown of Thorn outbreaks on the reefs In Taveuni, Fiji, both incidences occurred after devastating storm surf that decimated the reef and then literary legions of them appeared out of nowhere and almost overnight consuming new coral buds.  For other areas it may be nutrient rich water from run offs that cause an outbreak.

No matter how they have appeared an outbreak must be stopped to ensure the survival of the reef.  Not being able to go down to the corner store and buy sodium bisulphate, as well as using any other method of injection is daunting due to the proximity of their nasty, venomous spines.  There is also the fear of them doing a 23 leg lift off.  

Lest we forget, the most important factor is that during the throes of death, they would probably get stressed and emits a maelstrom of cross fertilization and compound the problem. So, we took a more primitive and practical approach to eradicating them.

Photos courtesy of Paddy Ryan 

*Roberta notes that collection the COTs in a plastic bag (as depicted in the photo is a huge "no-no". Once stressed the critters release all their reproductive juices into the water and plankton. They only need to be 6 feet apart to have almost a 100% fertility rate and in a bag you're guaranteeing they will multiply in abundance.