Ok I set up a 10gallon tank for them until I can get them back to the beach on the 19th. I found out that these crabs needed a area of dry sand so I filled up one side with sand, and filled the other with water. They burrow alot in the sand, and spend most of the time out of the water. They swim great though. I took out a few gallons of water out of the main, hooked up a little filter that came with the 10g. It makes a nice water fall. Well here are some pics.
PS. I used some reg playsand I found at the hardware store. I seeded it with a few cups from my tank, just in case they eat stuff like that.