Crown of Thorns Invasion - What to do ??

[calypsonick]

In the 5 years diving on the northern coast of Timor-Leste, we have run across an occasional crown of thorns here and there. Due to civil disturbances we have not been diving as much as we would have liked and went back to a popular dive site - Dili Rock after having been away for several months. What we saw was rather alarming with Crown of Thorns starfish all over the place between 4-12 meters in depth, sucking the life out of the hard corals. This picture give you an idea of what we were seeing. There were clumps of as many as 8-10 stars leaving big swaths of bleached coral in its wake.

As a no-impact diver, I tend to follow the minimal interaction with the marine environment model but it is hard to watch this invasion and do nothing.

I have heard of diver interventions regarding this kind of problem but do not know whether they are effective or not. Is there something divers can do to intervene or do we just let "nature take its course" ??

 

[PenguinAdLitem]

Fascinating. We don't have many diveable hard corals up here, so this was not a phenomena I knew anything about. I found this: http://www.aims.gov.au/pages/reflib/cot-starfish/pages/cot-000.html

According to it, there's probably nothing much you can do but wait - apparently a control program was attempted in Japan, and far from helping it may have resulted in a chronic crown of thorns problem there.

 

[Kwbyron]

Check with local authorities, you may be able to catch and kill them... I believe they are considered an invasive species with unchecked population growth. Be careful though, if I remember, they are highly poisonous and rather dangerous. I want to think the control methods being tried involved a stick that shocked them....

 

[Zeeman]

Dive knife. Gloves. cut open. feed to fish.



Z...

 

[Kwbyron]

ahh....but those yellow tips all over the guy? they can move them and they are long and sharp enough to piece your gloves...

 

[isurus]

Dive knife. Gloves. cut open. feed to fish.



Z...

I seem to recall reading that can trigger a sudden "death spawn" leading to more babies. They definitely regenerate if cut into pieces. In the Philippines I know they collected them and literally removed the whole animal from the reef as a means of control.

 

[Kupu]

I saw good results in the Philippines where divers collected thousands of COTs from reefs that were being overrun. A couple of years later there are still a few around but nothing like the number before divers intervened. I did a few collection dives using a big mesh sack, with a little practice it is easy to scoop them up with a stick or dive knife and push them into the bag. The fun part is watching them quickly dehydrate into a thin layer of slime once they are on the surface.

I'm not sure if collection is always a good idea, at first I was skeptical about participating in the collection since I had heard they could release lots of eggs if disturbed and prefer to let nature run its course. But in this instance I see only positive results so far. It seems like a shame to just sit back and watch a good dive site get bleached out from COTs when a bit of help from divers can make a real difference.

 

[Hank49]

I was in the Philippines in all of 1999 after the big El Nino which bleached coral world wide on a large scale. The west side of the island, which gets little tidal current, was over run with COTs. (the back side didn't bleach and didn't get infested with them). At first, we tried injecting them with chlorine. This was time consuming because to kill them, you have to inject all 12 arms since each one has a reproductive system. We then resorted to just gathering them and putting them into fertilizer bags, which we buried in a hole. All of this gathering had little effect though. The coral had mostly died anyway from the heated water and subsequent bleaching. One theory, which makes the most sense to me, is that once the reef bleached, it's natural defenses went down allowing the COTS to over run it. By the later part of the year, the COTs were gone and the reef was showing signs of recovery.
But yes, be careful handling them. I was poked on the ankle bone with little to no affect. But I got one in the tip of my thumb that hurt for two months.

 

[Cacia]

here, they inject them with isopropyl alcohol, I heard. (Syringes)

 

[Kupu]

I started looking around and found some interesting info on the Australian Institute of Marine Science (AIMS) site. http://www.aims.gov.au/pages/reflib/cot-starfish/pages/cot-000.html

It looks like control methods are usually ineffective. But if control methods are used in a small enough area (>1 hectare) on a regular schedule, it might be possible to keep them in check. I would agree that if a large area is already damaged from natural or man made reasons it is best to let it be and wait for nature to do its best. But if a favorite divesite is otherwise healthy and starts showing signs of being overrun by COTs, I would be tempted to do collection dives hoping to reduce the COT impact. It is tough to watch when a couple of COTs start moving across a table coral 3 meters in diameter and slowly suck the life out a little more each day when they could be plucked off at the beginning.