It definitely looks to be something just off shore. The IR pic is *really* interesting! I'm not sure what the yellow color would indicate here (any experts out there??)...
Since this object apparently is mobile and resides in the ocean, I would think it could show up anywhere along the coast... Could this bear any relation to that cluster of "things" that show up during the event that takes out the original rover?
My best theory for that particular event is that something breached the water surface at the western shore with sufficient force to flood the sand bar, deposit some bionts and then proceeded to intelligently disassemble the rover. Perhaps an intelligent automated system, perhaps an intelligent biont (and no, I haven't reached the end game yet, so I don't know if this mystery is answered in the end).