Once upon a time, huge underwater reefs made up of tens of thousands of oysters lined our coast. These reefs were ten or twenty feet high and kept the large waves kicked up by Nor'easters from hitting our coasts.
Each oyster on those reefs filtered 40 gallon of water a day, keeping costal waters clear. The reefs were home to plants, which spread and prevented sand and beaches from being swept out to sea. On top of that, the oysters provided a natural filtration which kept coastal water clear. Reefs sheltered hundreds of other species, dramatically increasing biodiversity.
Over time, those reefs were mined out for food or destroyed for convenience.