I've been meaning to document this for a while now. It is my observation that hermit crabs have their favourite resting places in the tank. Each night, they roam around, then return the favoured spot for the day.
Unfortunately for this particular coral, about 30+ hermits spend their days in it. This coral used to have a resident acro-crab, but he didn't survive the transfer to the new tank (or something got him). The acro-crab was quite good at fending off any hermit that attempted to get near his coral. The hermits are having a long term effect on the coral growth pattern of the coral as the areas they sit on don't get any light.
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400 gal reef. Established April, 2007. 3 Sequence Dart, RM12-4 skimmer, 2 x OM4Ways, Yellow Tang, Maroon Clown (pair), Blonde Naso Tang, Vlamingi Tang, Foxface Rabbit, Unicorn Tang, 2 Pakistani Butterflies and a few coral gobies
My Tank:
http://www.canreef.com/vbulletin/showthread.php?t=28436