...at the begining (by 1/19/2014 imagery date) there was darkness (at night),
then (by 12/16/2014 imagery date) they said; let there be light,
and there was light (long before 1/24/2016 imagery date). ... (:
Firstly I thought that ti was a small boat, then I have noticed the long shadow and realised; it is a vertical feature. After checked GE historical imagery became obvious it is not a simple "tall" buoy, but some higher equipment; a pole or beacon, fixed steady to the seabed.
I am not familiar with maritime navigation and cannot imagine, what else this could be than some kind of coast-light by the entrance of Dodge Island port.
I don't know much about this, either. (I could always ask my brother, the boat captain. ) There are a lot of markers around there leading, I suppose, to the channel at Miami Beach. I don't know if yours has a light, but it seems like the only very tall one and I'll bet it's a light. Also in that area I found a bright orange buoy and some other small structures that look like small versions of yours. Also, check out the photo that is near my first "buoy" label. There are others, but I didn't mark them all. The channel has to be very deep there for the heavy vacation cruise traffic.
Your second image is a good find - the construction crew building the light, I guess. I briefly google-searched for a light in the water there, but only found the lighthouse on land at Biscayne Bay.
Eva is alive and well on Ipernity, ... I am slightly acquainted with her! I will send her a link to this post, she will get a laugh from it. ...
How small this World is! Please let us know about her reaction in a reply to my DD thread! (;
Also forward my best wishes to her! My grandma has died last november at the age of 91, but hardly ever held a digital camera in her hands, not to upload fake images on web-map-engine databases... so different lives, so different ways on Earth!