Every successful reef aquarist must, at some point, face an inevitable question: should I cut this particular coral.  Problems between corals arise from invasion of space, shading, and other overcrowding issues.  The Montipora setosa pictured above has fallen into the shadow of a faster growing Acropora.  The shading is starting to slow growth in the coral below and if allowed to continue some tissue loss will result.  The Acropora is a fast growing variety and will completely over grow the slower Montipora in time.  Action must be taken, and cutting some of the branches will not harm the coral if done carefully.  These clippings can be attached elsewhere in the aquarium or traded to another hobbyist.  Trimming back the Acropora will allow the slower specimen to thrive, and the area where the branches are removed will regrow and not harm the coral.  Fragmenting is a natural process in our oceans and is done by fish, storm surges, and other natural occurrences. In a captive reef, you can start slow with trimming and, as you gain experience, it will become part of your normal maintenance and will not seem scary at all.