General Introduction and Study Aims

Seagrasses are marine flowering plants found in shallow coastal habitats around the world. They most commonly occupy sandy intertidal and subtidal areas to a maximum depth of about 10 m. Seagrasses typically grow in monospecific stands called ‘beds’ or ‘meadows’. These beds create a habitat of considerable importance from an ecological, economic and biodiversity perspective. The beds support a high density and diversity of associated flora and fauna, and provide valuable nursery and feeding grounds for fishes and birds. The binding of sediment by seagrass root networks also acts to stabilize the shoreline and reduce coastal erosion.

Before the early 1900s three species of Zostera, or ‘eelgrass’, were common in sandy coastal areas of the British Isles, but their abundance was severely reduced during the 1920s-1930s period by a ‘wasting disease’ that is still not fully understood today. Since this time there has only been limited and localized recovery of the Zostera beds. These plants flourish in accessible nearshore margins, and can therefore be adversely affected by many forms of coastal development, in particular dredging and excessive nutrient loading. Because of the value of seagrasses as a representative habitat for the UK, their high biodiversity and ecological importance, and their vulnerability to anthropogenic impacts, several parallel initiatives are now underway to better understand the role of these plants in coastal ecosystems and to facilitate effective conservation measures.

As described in the Preface to this report, this work is conducted through the auspices of the UK Marine SACs Project, as part of the implementation of the EU Habitats Directive. In this context, the three Zostera species occur in eleven of the twelve UK Marine SAC Project demonstration sites, and are key elements of five of the seven Annex I habitats for which marine SACs can be selected in the UK, namely:

  • Lagoons
  • Estuaries
  • Large shallow inlets and bays
  • Intertidal mud and sand flats
  • Shallow subtidal sandbanks

The objective of this report is to summarize and review the available information on these species in their capacity as a functional ‘biotope’ or community, addressing both shared and distinct features of these three species. The review focuses on the fundamental environmental and biological attributes of the Zostera biotope, its sensitivity to natural and human-induced change, and options for monitoring such changes that are relevant to the management of marine SACs. This report serves as a complement to, and a synthesis and elaboration of, two recent reports, prepared as part of the UK Biodiversity Action Plan, Davison (1997a) and Holt et al. (1997). The current state of knowledge of Zostera in Wales is summarized by Kay (1998). These three sources should be consulted for more detailed infomation on the issues covered in this report.

Nature and Importance of the Zostera Biotope Complex

Distribution and Status of the Zostera Biotope Complex

Zostera Biotope Classification