I took this picture while hanging over the edge of a concrete wall above the waters of the Tampa Bay in Florida. I was in Philippe Park in Safety Harbor.
A worldwide characteristic of rocky shores is the vertical layers, or zones, of animals and plants extending from the species that are almost always immersed to those that are only wetted by the highest tides or wave splash. Such zones are present even on shores where the tides are imperceptible (example).
In this case, there were apparently only 2 species present: a zone of oysters right at the edge of the water, followed by a zone of small barnacles. A closer look would undoubtedly have revealed additional species within those 2 zones.
Because the picture was taken from above, the original was upside down, which I reversed before posting here.