Haha - you just identified all crabs!
Mike, can you get a better pic of the carapace (body) from the top and from the front. It might be too young still to be able to ID. Young crabs may not show different characteristics yet, so can be hard to determine.
Not sure where they get their pods from, but if they are collecting pods from the ocean, this will include crabs. Crabs have a life cycle that includes being in the plankton zone as larvae and juveniles, before settling out on the bottom of the ocean or other substrate.