Gudmundur Geir's aquarium.

[Samper]

In the tank of the month on RC the owner shows two pics of his corals doing battle and has the following to say about it.

"The Hydnophora and the Acropora had a gap between them which I thought was wide enough to prevent competition, and they had been that way for months when suddenly the Hydnophora struck with the full force of its mesenterial filaments, killing at least a third of the Acropora. "


Could someone explain this phenomenon to me as it's the first time I've read or seen anything like it.

[kevinpo]

It is a defense mechanism for SPS corals and is very effective. Here is a picture of an A. grandis attacking the glass but could do the same thing to a coral it detects encroaching its space.

HTH,
Kevin

[Ninong]

I'm not sure if you're asking specifically about mesenterial filament attack or aggression in general, so I guess I'll cover both sweeper tentacles and mesenterial filament attack.

Sweeper tentacles are specialized tentacles with an extra helping of stinging nematocysts. They are feeding tentacles that differentiate in response to weeks of contact with corals of another species. They can be 5-10 times the length of regular feeding tentacles. They extend at night and flail around seeking something to attack. The two different species of corals do not have to be actually touching each other to stimulate the growth of sweeper tentacles, just near enough for them to "smell" each other.

Another structure which is used as a weapon of aggression or defense is the digestive mesenterial filament. Mesenterial filaments can be extruded through the body wall or oral cavity onto adjacent corals. They can damage the victim coral in two ways: (1) Digesting it, and (2) stinging it with nematocysts. Most authorities believe that digestion is the major mode of attack with mesenterial filaments.

Hydnophora is known for its aggressive capabilities. It will usually win the war with most other corals. Don't hold me to this because I didn't bother to look it up, but I believe I remember reading that their range is as much as 15 cm (6").

P.S. -- I forgot to mention that corals in the wild attack at night but corals in captivity will sometimes attack during the daytime, too.

[Samper]

That's very interesting to me. Is there a list somewhere listing which corals in captivity have done this which species they attacked? I just want to make sure this never happens in one of my systems.

[dougc]

I had an encrusting hydnophora that killed several nearby corals. It never attacked anything more than a couple of inches away. On the other hand, I had a green branching hydnophora that had star polyps and zooanthids growing up the base. It was pretty much a standoff, with neither gaining or losing ground. Maybe the encrusting types are more aggressive because they cannot carve out space for themselves by shadowing out competitors.

[Ninong]

That's very interesting to me. Is there a list somewhere listing which corals in captivity have done this which species they attacked? I just want to make sure this never happens in one of my systems.

I'm not sure I understand your question. All corals have defensive and aggressive capabilities but just as these capabilities vary in humans, they also vary in corals. Some corals are virtual black belts in karate while others are more like Peewee Herman.

Forget about the idea that you can "make sure this never happens" in one of your systems. It's just the natural way of things. You can manage it with judicious placement and careful maintenance -- pruning, etc. Some hobbyists have tried cutting off sweeper tentacles but that probably just delays things a little because new sweepers will form.

Sweeper tentacles have the longest range and their range varies quite a bit depending on the species of coral. Some may have a range of as much as 15-20 cm. Mesenterial filament attack requires closer proximity than sweeper tentacle attack and acrorhagi attack requires that the corals be virtually touching each other.

You need to get a copy of Eric Borneman's Aquarium Corals and read the section on "Behavioral Competition" beginning on page 70. In the meantime, you can find answers to all of your questions online provided you know how to google. Try to use words and phrases that sound "scientific." I have found that if I want to pull up the good stuff (academic papers), I need to enter the Latin names for animals and phrases that use a lot of 50-cent words for other things. For this particular topic, try running the following words or phrases through google and see what you get (look for academic hits, not hobbyists): mesenterial filaments, physiology of mesenterial filaments, mesenterial filaments for defense and aggression in corals, physiology of nematocysts, behavioral aggression in actinians, physiology of sweeper tentacles, acrorhagi, etc.

[Samper]

Thanks Ninong. I'll be reading.

[64Ivy]

Listen to Ninong; especially about placement. Below is another picture of what can happen when you don't. This is a hydnophora stinging a nearby Tricolor. In a few hours, the area 'entwinted' by the filaments will be literally melting off the skeleton. By the next day, all that will be left is the 'bare bones'.

Hydnophora is a beautiful coral but deadly to most others placed to near it. If this thing lived on land, it'd be a Steven King novel.

[Ninong]

Wow, Mike! That is a spectacular picture.

[Samper]

Was that your acropora that was damaged?

[64Ivy]

Was that your acropora that was damaged?

Yep, it was. Funny thing about those two pieces; the reason I haven't moved the Tri-color is because it is one of three 'spontaneous' daughter colonies I've successfully raised so far. Unfortunately, this one chose to grow onto a huge rock and trying to pry it off would either completely destroy it or cause great damage to that section of the tank. Remember that my tank has been up and running since 1995 ('SPS' dominant since 1999) and that almost all of my rockwork has been literally fused together by either coral encrustation or layers of old epoxy. So I have no choice other than to frag back the hydro, which I occasionally do.

The strange part is that these two have been 'fighting' off and on like this for over a year now. Every so often, the hydro will reach out like this and kill off a small section of the tricolor. I will then break off this dead section. A few months later the tricolor will begin to grow at that spot again and when the hydro has had enough, it will reach out and kill it again, starting the process all over again. Even stranger is that the Tricolor will not show ANY other growth except at the area nearest the hydro...where it will enivitably be killed.

As they used to say on "Laugh-In", look THAT up in your Funk & Wagnalls!

[Poseidon]

That is a very cool picture... I wonder if the Tri Color was "upstream" would the Hydro still be able to get it?