I have a very happy six inch Crocea clam living in my tank. This clam's shell is about fifty percent covered with Galaxea coral. Will this coral damage the clam in the future? Is it possible to remove the coral with out damaging the clam?
First of all, a happy clam is always good to hear about.
Coral growth on clam shells does not appear to be detrimental in any way to clam health. In fact, this occurs in nature all the time. However, there are a few things to consider. A lot of LPS corals have particularly vicious nematocysts to fend off other corals. These may or may not sting your clam's mantle. Some do, some don't. And, croceas in the wild typically have nothing growing on their shells since they would be almost completely lodged in coral or rock at that size.
If your coral inhibits light to the clam mantle, it obviously must go. Watch the edges of the mantle that touch the coral - has the flesh in these locations retracted any or show signs of damage? If it has, the coral must go.
You can accomplish this many different ways. You could remove your clam from the water (On his side!), and scrub the coral with a toothbrush or similar tool - then rinse away what you scrub. Yes, a good shell scrub/massage will kill the coral.
But, if your clam is happy, don't bother him. Just keep an eye out.
I agree with all that was said above. I have had an incidnet where a frogspawn (euphyllia divisa) sent out a particularly long sweeper tentacle. The tentacle came in contact with a large derasa (about 10") mantle. The euphyllia caused no visible damage, but the clam was obviously irratated as it would pull back its mantle in the area where the coral would contact.
As stated above I would base removal of the coral strictly on observation. I personally dont have any galaxea stocked in my tank, but I do know that it produces very very long sweeper tentacles laden with nematocysts. If the mantle looks grea but is retracted in very small tight areas then the clam is getting irratatedand the coral must be removed. Good luck!!!