Saltmarsh and Estuarine Habitats

We tend to create an imaginary divide between freshwater and marine habitats, and yet there are large areas of our coast and river where the two mix. Freshwater springs flowing into rockpools from under our chalk cliffs, and rainfall onto coastal mudflats is important in helping to shape the ecology of our estuaries and coast. We need to think more about creating the economic, social and political systems which allow us to manage our coastal and river landscapes as a functioning whole. This includes acknowledging that rivers need to be allowed to be connected to our seas.

Saltmarsh is one of the main habitats found around our river estuaries. Saltmarshes create an important transition zone between the sea and the land. This rare habitat is found at only a few places in Sussex: mainly at the harbours of Rye, Chichester and Pagham and along the tidal reaches of the Rivers Rother, Cuckmere and Adur. Sussex has around 400 hectares of saltmarsh. Over 92 % of this is found in West Sussex, with the majority found in Chichester Harbour, the largest saltmarsh in the South-East region. Much of the saltmarsh in Sussex is of recent origin, formed since the rapid spread of the invasive common cord-grass (Spartina anglica).

Current threats to salt marshes include land reclamation for farming, recreation, housing and industry; boating and erosion by walkers; engineering works such as dredging and the construction of river and harbour training walls which limit the amount and distribution of sediments reaching a saltmarsh.

Sea level rise and climate change is also a threat, particularly if the landward edge has been fixed by human development creating ‘coastal squeeze’. Southern England is currently subsiding by around 0.7 mm per year. (Andy Cundy, 2010). In the South, the vertical accretion of sediments in saltmarshes is more or less keeping pace with current sea level rise, and as such, it helps to buffer the effects of coastal flooding caused by climate change. Recent rates of sea-level rise along the Sussex coastline may however be in excess of 4 mm yr-1, which is driving some rapid changes in coastal marsh habitats.

Saltmarsh - natures flood defence

Saltmarsh can make an important contribution to coastal sea defences, with the added benefit that they are natural and economical when compared to ‘hard’ (man made) defences, and that they are fantastic habitats for wildlife. If the area of saltmarsh is large enough it can remove all of the damaging energy of an incoming wave under certain conditions. Approximately 50% of the wave energy and 40% of the wave height can be removed by the first 2.5m of saltmarsh, and saltmarsh plants can assist the natural accretion of coastal sediments (French, 2001).

What wildlife might you find in saltmarsh?

Saltmarsh is sometimes seen as ‘unsightly’, with lots of exposed mud and less of the more charismatic and flowering plant species. Appearances can be deceptive however, and it is in fact one of the richest habitats in the County.

Saltmarshes are an extremely important food resource for breeding and wintering wading birds and wildfowl. They support internationally important numbers of Sussex bird species, as well as providing nursery sites for several species of fish. Areas of saltmarsh with high structural and plant diversity are also important for invertebrates.

Some of the species that you might expect to find in Sussex saltmarsh include :-

  • redshank (Tringa totanus),
  • bass (Dicentrarchus labrax)
  • shore crab (Carcinus maenas)
  • starwort moth (Cucullia asteris)
  • sea aster (Aster tripolium)
  • glasswort / Marsh samphire (Salicornia)

Saline lagoons

Research suggests that Sussex has only 13 saline lagoons covering an area of just under 65 ha. Only three of these are considered 'natural' lagoons. Natural coastal lagoons would have been much more common in the past. These fascinating coastal pools such as those found at Rye Harbour are often tidally influenced and provide unique niches for unusual coastal species.