12 corals were selected with Coralliophila violacea.  A random snail was selected, and a similar location identified on the coral for comparison.  At each location, a 20cm by 20cm plexiglass plate was placed against the coral, and 20 randomly selected depth measurements taken.  The variance of those measurements is reported.  A nail was then hammered into the coral at each location, and the length recorded.   After 1 year, the corals were revisited, and the measurements repeated to calculate change in nail length (coral linear extension) and change in morphology (change in variance of depth measurements).