[Chirashi]

If I had to guess, I'd say it is just coralline algae. Is it 3-dimensional? It's very hard to tell from the image.

P.S. If you own a regular film SLR camara, I found recently that the close-up diopter lenses (the kind that screw onto the front of the regular lens) work if held in front of a digital camera -- you can get really close and in focus. Maybe you can get a better image that way...