The seaward margin of the Hythe Spartina Marshes is characterised by whitish beach ridges of shells. Similar features occur in various parts of the world, including the Mississippi Delta where they are known as "cheniers". The cheniers at Hythe are moving landwards and joining to form more continuous ridges. This can be seen in comparative aerial photographs from 1968 and 2007 above. The 2007 aerial photographs are courtesy of the The Channel Coastal Observatory , National Oceanography Centre, Southampton.
The cheniers or shell beach ridges at the Hythe Spartina Marshes have been discussed by Quaresma in a thesis (2008) and in a paper by Quaresma et al. (2007). The shells are of Cerastoderma glaucum (or C. edule?), a common, shallow-burrowing, edible bivalve, known in Britain as the "Cockle". They live in the intertidal mudflats but the dead shells are eroded out and transported shorewards as bedload during the early flood tide. Shell transport rates can reach up to 0.7m. per tide over the upper mudflat, according to Quaresma et al. Shell-induced erosion can become an important parameter on morphological changes of a coastal area. Shells are transported over the mudflat, deposited at the base of the cliff, and eventually transported over the salt marsh where they form the extensive chenier deposits, shown above. The Cerastoderma shell cheniers move over the saltmarshes only during storms, but at such times they can move up to 3 metres.