Aeriel view of Bull islandSalt marshes occur in coastal areas between the upper levels of the spring and neep tides. They are periodically submerged which means that the plants living on the marsh must be able to tolerate a wide range of conditions, from inundation in water to open, dry air. For this reason, different plants tend to grow in different areas of the salt marsh.  Salt marshes are very important as they act as buffers, protecting shorelines from erosion. However, salt marshes are also subject to severe erosion themselves, as increasingly roads and other infrastructure are built on them.