Quote from the article linked by Charlie:
The Eponymous Bubbles
The bubbles on the bubble tip anemones are quite attractive. Don’t get too attached to that look. They seem to come and go with time. In my experience, most BTAs do not regularly display bubbles except perhaps when disturbed. Bubbles do not seem to be an indicator of health, reproduction or anything other then maybe rough handle (as during collection, shipping, etc.)