silver ball thing growing

Question
We have a 46 gallon saltwater tank that is in great shape. It's been no problem for over a year. Lots of new stuff popping up all over. We have multiple plants, crabs, shrimp, fish, snails and more. A silver round ball is growing on a piece of live rock it's the size of a quarter. Any idea what this might be? It's very pretty and almost looks fake. Thanks for any help.

Answer
I am pretty sure it is bubble algae. It looks silver because of the lighting on the tank. It will take over your rock if that is in fact what it is. Here is a link for you to ID. Do you have emerald crabs, they should take care of it. here is the link, http://images.search.yahoo.com/search/images;_ylt=A0geu6qa2HdGJmgB7TBXNyoA?ei=UT...