Mixed-Marl prairies occur on areas of thin calcitic soil which overlays a limestone bedrock. The calcitic soil is formed by submerged periphyton. In short hydroperiod prairies, inundated for 3 to 7 months, periphyton grows below the water line where there is adequate sunlight. This is in contrast to the longer hydroperiod prairies where periphyton is able to grow on the surface of the water. In these short hydroperiod prairies, the water contains a higher amount of dissolve calcium which is incorporated into the periphyton by blue-green algae.
When the periphyton dies back the calcium crystallizes and re-forms the calcitic soil crust as the organic material quickly oxidizes. These prairies are dominated by a by hundreds of grass species including muhly grass (Muhlenbergia filipes), thin stands of sawgrass (Cladium jamaicense), and black-top sedge (Schoenus nigricans). This habitat is ideal breeding habitat for the Cape Sable Seaside Sparrow.