Explanation: To my VERY limited understanding, these mounds were a way of turning the mass debris from fishing and aquaculture (shells) into something somewhat useful (pier-like extensions into the water) instead of just a junk pile tossed inland. Very neat stuff!
It’s a fascinating window into a time/place we know little about. Wikipedia has a short article:
the bulk of the mounds were clean shell deposits, almost entirely made up of small oyster shells, which had been placed on submerged mud flats. Based on dating of potsherds found at the site, Sears concluded that the residents of the site had lived on the edge of the river, moving the village towards the water as the mounds built up behind them. All of the potsherds collected at the site were assigned to the Glades I and II periods, placing occupation of the site in the period from about 200 or 100 BCE to 800 or 900 CE.
Florida used to be civilized.
