Crown of Thorns

Hi fellas.

I've been wondering about crown of thorns starfish lately. I hear that they could easily consume and wipeout coral colonies. They could be even more destructive to corals that humans.

Well if what i hear is true, then why do we leave them alone. Shouldnt we do something about them like i dunno take them out of the water or something? Cuz conservation of corals doesnt make sense to me with these guys around.

But hey what do i know. <_<

What do you think, guys? Correct me if I'm wrong.

Hi Skroob,

They do pop up in areas at times as major scourges, mostly due to "us humans" interfering with nature. One of the major natural predators of the Crown of Thorns is the Triton trumpet shell mollusc, unfortunately these get harvested a lot...cuz hey! its a pretty shell, lets sell it to tourists...also, a lot of COF explosions are the result of weakened coral due to erosion and such things.

In a lot of areas there are COF clean ups when they pop up in numbers. There are a couple of ways to do this. One is to use chemical injection, another is to collect them on spears and remove from the water...i am sure there are others.

But, they are a part of nature and do serve a purpose (who knows what...but probably something akin to a forest fire) so getting rid of them completely would be inappropriate and irresponsible.

I will move this thread to the Environmental section

Mike

Yep, the crown of thorns starfish has coexisted with coral in the ocean for millions of years. It was not until we started F'ing with the environment that they became a problem.

Most of the time the population of COT stars is normal and healthy. When you see a few on a dive, that is nothing to worry about. The star's are not the only coral preditor you see on an average dive. Most of the butterflyfish, angelfish, parrotfish and a lot of other fish eat coral for the majority of their diet. Destroying every COT starfish in the ocean makes no more sense than killing every angelfish and butterfly fish for the same reason.

The problem is that every once in a while there is a bloom and the COT starfish population increases 10,000 fold. You can hardly see the reef through the mat of starfish. In a few days they consume nearly 100% of the prey coral. They then starve to death and die natural and the reef can repopulate. Even this, like coral bleaching may be a natural event that happened pre-human but the problem with both of these (bleaching and starfish) is that the frequency of occurrence is increasing.

There are several theories as to what we have done to cause the blooms but all theories include us f'ing up the environment so in the end we are still to blame.

We found a herd of COT near Wakatobi last year. I was suprised at their ability to navigate even the delicate Acropora and suck the life out of it (see image) I don't remember if the COT hit the plate/stony corals as bad as these branching corals. I was also suprised at the size, about 60cm accross the arms and the spines ARE sharp.

So, I understand that COTs are healthy only if the environment is balanced. However, our environment is pretty messed up and the natural enemies of the COT is decreasing in populations due to being harvested regularly.

So, I guess something should be done to decrease the population of COTs. Right? Which means that whenever I see 2 crown of thorns I should kill one of them to bring balance to the galaxy and save it from the tyranny of the dark side.

Am I being extreme or responsible? I have no idea.

No, when you see two, there is no problem. When you see 200 you can kill them.

Am I wrong ?

My understanding is that COT are a a highly mobile species in a larvael stage , and that by the time you can see them all you can do is at best contain them !

Crown-of thorns starfish begin life as a tiny swimming larvae and settle onto coral reefs at the size of only 0.5mm in diameter.

These small starfish feed on algae and live amongst dead coral rubble teeming with large numbers of other animals, including predatory crabs and shrimps, which may eat the small starfish.

As they grow, the starfish must emerge from the protection of the coral rubble to feed on live corals. When they do this they expose themselves to other types of predators, such as fish.

We need to know what types of animals eat small crown-of-thorns starfish, and at what rates they feed.

This is the information that will enable us to understand the important factors which effect the numbers of starfish which actually survive to adulthood on reefs on a global basis.

I do recall being spiked many times while trying to kill ( remove ) one of these things. Quite an inconvenience as I recall.......

Cheers

Peter

No, when you see two, there is no problem.  When you see 200 you can kill them.

<{POST_SNAPBACK}>

This is similar to California water where sea urchins ruin kelp communities. It is a balance: when the kelp is gone, the urchins die, the kelp comes back, the urchins come back. I don't feel a bit bad when I kill an urchin since there are thousands in a small area.

Joe

I might be wrong here, but I heard that you have to kill the COT in a special way. Don’t just put your knife into it and chop it to pieces because they reproduce if you do so.

Am I right or wrong?

One of the most beautiful and popular dive sites (Careless Reef) in Hurghada got eaten up by COT. It’s around 6 years ago and the reef is slowly growing back to its former glory.

This is similar to California water where sea urchins ruin kelp communities.  It is a balance: when the kelp is gone, the urchins die, the kelp comes back, the urchins come back.  I don't feel a bit bad when I kill an urchin since there are thousands in a small area.

 

Joe

<{POST_SNAPBACK}>

It's was the same when I worked in Gran Canary. We killed sea urchins every dive there. The puffer fish which is more or less the only fish around the island that eat the urchin is close to be exterminated. We even had a guy from the fishery department in Las Palmas at our dive school one day telling us all about it.

I might be wrong here, but I heard that you have to kill the COT in a special way. Don’t just put your knife into it and chop it to pieces because they reproduce if you do so.

 

Am I right or wrong?

=================

Hi Pedda,

 

Correct, at least according to our guides. They said the adult stars contain larvae or fertilized eggs (constantly?) that could escape if punctured. We were advised to drop them into deep (40m) water where the large napoleon wrasses would eat them. One diver said he helped an official project where they hauled the COT to shore and burned them by the boatload.

Some starfish can reproduce from an arm. If you break off an arm and it has a small piece of the central disk on it, the arm will grow a new body. We see them all over here in California....one long arm (ray) and a body. The COT and other sea star species are pretty robust aminals, which is one reason they are so dominant and hard to kill, although this is not the only reason. Food must be present and conditions right. I mean, afterall, you wouldn't find a COT in California would you? These days, who knows what can happen. El Nino brought many un-natural animals to southern California from the warm water of Baja. Most are gone, but there are two Scythe Mark butterfly fish living at Ship Rock off of Catalina Island still today.

Joe

One method that people have used in Komodo is injection with a copper sulphate solution. I've not read any of the scientific literature on the subject, but this approach is said to be effective. The copper sulfate solution is in a plastic container, attached by a hose to an injector (with a fairly long tip, to avoid exposing operators' hands to the spines) that injects a measured dose.

Frogfish

I knew one day my affection for the National Geographic Channel would come in handy!

These small starfish feed on algae Someone touched on the answer here but according to the documentary I watched, here is what they found. Again the bread trail lead back to us human beans which isn't surprising. They've discovered that the COT blooms usually occurred after a major period of heavy rain and water run off. This washed chemical and natural fertilizers off of farm land into the rivers and eventually into the ocean. Immediately following this an algae bloom would occur. The normal survival rate of COT Larvae is very small due to the natural predation and competition for food. However, with abundant food, the Larvae matured rapidly into young adults who have virtually no predators other than Snails. Hence you get a COT bloom.

Killing them. In many areas they are hiring divers to assault them. The ONLY way to kill them is to inject every leg and the main body of the starfish with a chemical poison. If you cut off a leg...you create another starfish. They simply regenerate the leg, and if I recall correctly the cutoff limb will generate into another COT as well. So unless you're armed with the correct killing device, you might be doing more harm than good by attempting to kill one with a knife. Furthermore, the spines on the COT are supposedly toxic to humans...handling one isn't the best of ideas.

Take care all!

Gary

But what if i run into a COT by chance? is there a special way of handing them?

I'm thinking of the old "stick a knife into its body and take out of the water" method. Will it work or will it release countless fetilizes eggs as scubaskeeter sez? Of course we dont have napoleon wrasses in the arabian gulf so we cant just drop them in the abyss.

Happy Eid!

Saad

I was once Witness to a "COT Hunt" in Egypt where several Hundreds was at Shab el Erg.

The way to kill them there was: put the into Boxes using a metal Hook (that are normaly used to store dive Equipment), Take the boxe to the Boat, Bring them in and leave them in the Sun to Dry.

Not very nice but Effective.

Simon

Yes...that would be effective..haha. BTW, a leg won't develop into a starfish but stabbing it with your knife will only slow it down...not kill it. Since the animals are not asexual, releasing eggs prematurely from one wouldn't increase the population.

If someone could just come up with a nice culinary dish made of the COT, human predators would take care of the rest.

hahaha....

A COT tandoori would make a nice special. Mmmm...