Seagrasses are one of the few flowering plants known to live in the sea. All three species of seagrass are considered nationally scarce. Dwarf eelgrass is found highest on the shore, often adjacent to lower saltmarsh communities; narrow-leafed eelgrass on the mid to lower shore; and eelgrass predominantly in the areas below the low tide mark (the sublittoral). The plants stabilise the substratum, are an important source of organic matter, and food particularly for wildfowl, and provide shelter and surface attachment for other species.

Much less is known about these species than their counterparts on dry land. However, it is known that they have suffered a severe population decline in the 1930s as a result of disease.

Since the 1930s outbreak, seagrass populations have only made a partial recovery and the disease is still thought to be present in the South West. Seagrasses are present in all their native habitats in the region, including saline (saltwater) lagoons such as The Fleet, estuaries, such as Salcombe and the Fal, and sheltered bays, such as Torbay and the Isles of Scilly.

Within the region's estuaries and saline lagoons seagrasses are known to be a vital food source for brent geese, whilst in the more saline conditions of sheltered bays, the soft sediments in which seagrasses typically live are known to support rich communities of burrowing animals. Some sites in the South West are also known to be important as a nursery area for fish and cephalopods, such as cuttlefish. Unfortunately, many South West sites consist of small fragmented populations making them more vulnerable to total loss.

Sites within the region which support seagrass beds are known to occur in estuaries, on the open coast and in saline lagoons. However, the distribution, extent and quality of the South West seagrass resource or the current range and severity of impacts affecting regional populations is not fully known.

The largest populations of Zostera species are undoubtedly those occurring in the Isles of Scilly and the Fleet lagoon.

Examples of seagrass species which occur on the short (s), middle (m), and long (l) lists in UK Steering Group report, for which a UK species action plan has been prepared (*), or which are characteristic of the habitat:

The main problem has been that seagrasses suffered a severe decline during the 1930s following the spread of a wasting disease. This disease, a slime mould called Labyrinthula, is still present and may result in the future die-back of stressed populations. Unfortunately, the current lack of information allows for little analysis of population fluctuations.

This has combined with other pressures such as coastal development including coast protection and, ironically, beach cleaning; pollution and both dredging and dumping.

Because of our lack of knowledge about seagrass beds much research is currently being carried out that should help us provide better protection of these sites and the wildlife that depends on them.

Seagrass populations in the Isles of Scilly are being monitored annually by Coral Cay volunteers under direction from English Nature. These studies have involved aerial photography and are recording changes in the extent of the seagrass populations.

Volunteer studies are also underway examining the extent and condition of seagrass throughout the year in the Helford estuary. This is being co-ordinated by the Helford Voluntary Marine Conservation Area Working Group. The Department of Biological Sciences of the University of Plymouth is currently instigating a varied programme of on-going research in the Yealm and Salcombe/Kingsbridge Estuaries. The World Wide Fund for Nature has recently been conducting research in the Fleet as part of a wider study of saline lagoons, which incidentally covers the populations of Zostera.

A two-year project is currently underway in the Fleet lagoon, looking at seasonal variations, population dynamics and reproductive phrenology and strategy in the Zostera marina var. angustifolia population. The aim is to increase understanding of the natural dynamics and reproduction of Zostera populations and to relate these to laboratory studies on seed biology and germination requirements to enable a platform for successful re-seeding programmes to be established.

A site on the Welsh side of the Severn Estuary is being monitored in connection with the Second Severn Crossing.