The homescar of a limpet would be a perfect answer for the circles, if the place wasn't so far from the tidal zone. They don't come so high and far away from the water. Only very high waves can reach this place. However, I could imagine a loose limpet being tossed away by some very powerful wave ending on this place. Or maybe somebody has brought a limpet there.
A man made origin, like some sort of stand or support with metal feet is another interesting and plausible answer to the riddle. It could have been from some military installation, because the whole Pula area has been fortified as the main naval harbour (at first built and founded as österreichische Kriegsmarine oder k. k. Kriegsmarine) for over a century. Many forts are still present.
The spot in the photo marked with yellow question mark looks like a man made artifact.
The photograph below is taken at the same place, a few feet further. Red outline is a possible dinosaur footprint.
The naval base in Pula in 19th century.
