Solent Habitat – Spartina Saltmarsh

Spartina Anglica
Spartina Anglica – Image by Jürgen Howaldt (licensed for reuse under a Creative Commons Licence)

Cordgrasses, known scientifically as Spartina Anglica, occupy the lower shore areas of the coast at depths which are regularly covered at high tide. They offer coastal protection and create intertidal land; by trapping sediments they also increase the elevation of these land areas and stabilise sediment, thus aiding in the creation of new saltmarsh areas. Spartina has high productivity and its growth and decay flux large amounts of energy and organic matter through the estuarine ecosystem. It lies at the base of the Solent saltmarsh food web and is a possible food source for many organisms. It creates a characteristic habitat which offers shelter and sustenance to a wide range of shallow water and intertidal animals and plants.

Yar estuary - 1948
The River Yar estuary, Isle of Wight in 1948. Note the lack of Spartina saltmarsh
Yar estuary - 2017
The River Yar estuary, Isle of Wight 2017. Note the extensive additions of saltmarsh

The first appearance of Spartina occurred as a hybridisation in Southampton Water sometime prior to 1870 and it spread rapidly by seed to Lymington and the Isle of Wight by the end of the 19th century. However, from the mid 20th century, there has been an almost equally dramatic loss. This erosion generally takes two forms; the erosion of the seaward edge of the marsh as material is washed away and secondly internal destruction of marsh areas by the widening of channel margins.

What sort of future habitat do we want and can we influence future events? If the Solent loses its Spartina saltmarshes, it seems that these areas will not return to the original open mud habitats of the 18th and 19th centuries, but the Solent coastline presently protected by saltmarsh will suffer extensive and quite rapid erosion. It is worth considering why the mud flats will not reform. Part of this reason may be that fine sediment is no longer flowing into the Solent in the quantity it once did. It is also possible that dredging, as well as the wash created by boats and shipping wave action may have decreased the tendency for fine silts to settle in the Solent.

As humans, we have an extraordinary ability to alter the natural world and frequently do so in adverse ways. However, when confronted with major ecological events such as Dutch Elm disease and Spartina die-back, it is notable how passive and fatalistic we have all become. This need not be the case and using our science and engineering skills, we can reverse ecological change. There has been considerable debate about the reason for the die-back, one of which is the development of areas of algae created when nutrients such as nitrogen and phosphorus are increased by human effluents. Spartina changes the habitat and in part is self-destructive by reducing sediment permeability. This leads to the conclusion that like almost all organisms, it needs constant new habitat– but without the fine sediments for it to colonise, the question must be asked of those who take actions to stop the flow of sediment down our rivers. Also to those who dredge and remove the sediment thus impacting on mudflat availability. The amount of oil residues found in Solent sediment is considerable and needs to be greatly reduced.