As long as you have enough for them to eat they should be fine. If there isn't enough to eat then they'll die. I have 2 in my tank, 58gal, and could probably have 1 or 2 more.
You known if it a problem as the clam will start to close up some. You also need to worry not just about them touching each other but sometime if they close enough they'll give off chemicals and start a chemical war which can be just as bad as them touching and sting each other.
Here is a good place, not only to buy, to find alot of good information about clams. They have a board where you can ask questions and look at prior anwser to questions.
I had problems with emerals picking on SPS. I actually watch one rip out polyps from a milli colony, just before his demise there is a thread on RC about emeral crab behavior.
Jhale, thanks for making the morning early. Hope you like the frags -
Careful with Zoas and clams, they will grow onto them and eventually kill the clam. If they grow onto the clam (like my crocea) keep a close eye on them.
Jim, My wife Cindy will give you a call tomorrow to pick up the mysis and the cylopeeze.
Jhale, I always had at least 6-8 emerald crabs in my 150 and 180 reef tanks, never notice them harming anything (including the bubble algae). Some of them are living in my acros like an acro crab. All of mine are from Florida.
Here is a picture of some of my clams from about 4 months ago, the three on the lower right are covered by green zoas and now I can?t see any bare shell on them anymore. They have been attached to the rock like that for about 18 months, all three don?t seem to be bother by the zoas and continues to grow. Be warned, you can?t get the zoas off without doing damage or stress to the clam, so once you let them grow on it, it will be pretty much permanent.
i have emerald crabs in my tank and sometimes it looks like they're blindly picking at some of my sps.it almost looks like they're feeling with the claws and once they feel a polyp they try to pull. i never really saw any do any real damage though, the polyps retracted everytime.
well I moved the clam, it's far away from the zoa's, I moved it to get more light.
just the other day I saw one of the little green crabs sitting in a birdsnest picking away at it. the coral was all closed up. I used a chop stick and scared the crab away, grrr. I have my eye on that crab now. I can't tell if the crab did the coral any harm, it opened up again and looks the same. dumb crab.
I only have one emerald crab and I am looking to get a few more. I think mine was quite an aggresive aglae eater.. I think... I see it picking at something all the time.. But do you know if the bigger emerald is better or the younger one??