I don't know about beardies, but in the Galopogos Islands iguanas have evolved to swim in the ocean and graze the algae growing on the rocks. I'm not sure about what sea plants might be healthy, though. What about the salt content?
Bearded dragons don't live naturally anywhere near salt water so i don't think they would be atuned to eating seaweed naturally, just my opinion anyway.
Mirage came out of brumation on April 26. He was doing great. On May 2 he started acting funny. We just redid his tank, and he keeps going into one of his hides. He just lays there. He shows no intrest in food. HELP!