Particular attention needs to be paid toward coral aggression when considering new coral purchases as well as placement.  When certain corals are placed in close proximity or as they increase in size naturally their aggressive nature manifests itself and can be problematic.   Corals have specialized mechanisms developed for protection and competition which include sweeper tentacles, mesenterial filaments and terpenoid compounds.

Sweeper Tentacles:

This is the most common defense mechanism found in the hard corals but also occur in some soft corals.  These tentacles are not the same as normal coral polyp often being many times longer and containing specialized stinging cells.  The effect of an attack on competing corals is that they can burn it to the point of severely damaging or even killing it.

Mesenterial Filaments:

These filaments produced by certain corals in their stomach can attack others in a way similar to digestion.  Corals of the genera Favia, Favites, Scolymia, Pavona and Cynarina all have this ability.

Terpenoid Compounds:

This is the method of battle employed by soft corals whereby releasing compounds into the water to impede the growth of neighboring corals.  By taking over additional space and growing above other corals they may result in blocking out the light and thus killing underlying coral.

Plan ahead when putting corals into your reef environment to avoid overcrowding and or aggression.  This should include providing adequate spacing and reducing tip over potential.  Make sure coral is securely attached before it has a chance to fully encrust is important.  Also care should be taken when removing or relocating corals.  This will reduce the likelihood that one coral will come into contact with another causing burning that can cause injury and become infected or potentially kill the colony.  Pruning or fragging over time may be necessary to keep proper spacing and avoid coral wars from erupting.

LPS:

It is recommended to provide a 4-6 inch zone in all directions.

SPS:

2-3 inches is generally enough however since SPS are fast growing extra space should be allotted for this.

Polyps & Soft Coral:

For the most part soft corals do not burn one another as bad as hard corals however there are a few considerations to take note of.  Faster growing corals will overgrow and may starve out slower growing corals.  Water flow is important so that their terpenoids do not linger and can be removed through filtration mechanisms.