World War III: In Your Fish Tank

Deadly Sweeper Tentacles can Sting Other Coral


Aquariums are so relaxing, so tranquil, so incredibly peaceful. You see the colorful marine life lazily drifting around, seemingly without any care in the world. Add to that scene gently swaying plants and lovely coral and you’ve got the picture of harmony.

Actually, that’s not true at all. That’s just us humans reading what we perceive as harmony, when in fact aquariums can be contentious battle zones. Fish and other wildlife are frequently fighting over territory and food, even though they’re in a controlled aquarium where their survival isn’t really threatened. But creatures of the deep can’t help it because they’re programmed to act this way.

At first glance, coral appears to be the single most nonthreatening creature in existence. It looks like a rock, or perhaps a hardened plant, so where’s the danger? Despite their seemingly harmless facade, coral are battle-ready warriors who are ready to enter war with neighboring coral.

Sweeper Tentacles Extended From a Coral


That my friend, is a cluster of sweeper tentacless. In the world of coral warfare they’re the equivalent of a drawn sword. From a human perspective, it’d probably be better to describe it as a bee on the end of a stick. Hard corals send out sweeper tentacles to scout for competing coral, and when they detect something they attack with stinging cells called “nematocysts.” These sting cells contain an alkali that’s pretty similar to bee venom, so their basic strategy is to sting enemy coral until bites the dust (or sand, in this case).

One of the craziest things about hard coral is that they’re capable of detecting enemy coral that are nearby. You could have a coral in your tank that doesn’t have any sweeper tentacles whatsoever. If you add another aggressive coral species to your tank, you will probably discover that your previously docile coral will start arming itself by developing sweeper tentacles in the direction of its perceived enemy.

A Coral Attacking a Nearby Hard Coral


Coral also use a battle strategy similar to what you might see on land. Trees have been known to use chemical warfare on other plants (yep, believe it or not — it’s true) in order to stunt their growth. That gives the aggressor tree an opportunity to grow more quickly than its competitors and soak up more sunlight and “starve out” their competitors. Some species of hard coral do the same thing, releasing harsh chemicals into the water that can stunt the development of other coral. The aggressor is then allowed to expand and soak up more resources.

So, How Can You Keep the Peace?

You need to think of yourself like NATO or similar international organizations, doing the best you can to stop violent aggression without disadvantaging any coral. The easiest way to do that is to simply keep coral far apart from each other. That old phrase “good fences makes good neighbor” also more-or-less applies to aquatic life.

A Heavily-Populated Coral Aquarium


The second thing that you’ve really got to watch out for is tip over. That’s when one coral gets too big for its britches, breaks off, and falls onto another coral. That will result in a stinging war between both of the coral, and there’s a good chance that they’ll both kill each other before you can stop them. You should be mindful about placing coral above other coral, and make sure that your coral can get a strong anchor.


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