^ Thanks for taking all the great pictures! (btw, I hate the unstoppable slideshow presentation. I wanna click on a thumb and stay locked in the big pics with left right arrows to see the next)
Those steel thingys are temporary wall braces of some kind... possibly submerged wall bracing for setting shorefront walls. Kind of like braces for basement walls up north but this is more florida centric. Note the loops at the end of each one. Looks like something to be secured to the subsurface with giant 'nails' or posts.
Regardless, the steel thingys are old, used and rusty. They are temporary construction 'braces' of some kind. Above is just my best guess, knowing what is coming.