I have an Iittala Aalto-tray with a candle and glass beads in the livingroom. I threw the smaller sea shells with the beads, and I'm really happy about the result.
I happened to have a small glass jar with air bubbles. I put the rocks on the bottom of the jar and sea shells on top. I also had a really old brown "bling" jewel in the sea shell box, so I threw that into the glass jar as well. It almost looks as if the sea shells are swimming in bubbly ocean water, don't you think? :)