Biodiversity & Conservation

Zostera noltii beds in upper to mid shore muddy sand



Image Mark Davies - A bed of Zostera noltii with Hydrobia ulvae visible on the mud surface. Image width ca 40 cm.
Image copyright information

  • #
Distribution map

LS.LMp.LSgr.Znol recorded (dark blue bullet) and expected (light blue bullet) distribution in Britain and Ireland (see below)

  • EC_Habitats
  • UK_BAP

For a list of 2004 characterising species please see the JNCC website.

Species indicative of sensitivity

To assess the sensitivity of the biotope, the sensitivity of component species is reviewed. Those species that are considered to be particularly indicative of the sensitivity of the biotope, and for which research has been undertaken in detail are shown below (see selection criteria). The biology of other component species of the biotope is also taken into account wherever information is known to the researcher.

Species found especially in this biotope

  • Rhodophysema georgii
  • Halothrix lumbricalis
  • Leblondiella densa
  • Myrionema magnusii
  • Cladosiphon zosterae
  • Punctaria crispata

Rare of scarce species associated with this biotope

  • Halothrix lumbricalis
  • Leblondiella densa
Community Importance Species name Common Name
Key structural Zostera noltii Dwarf eelgrass
Important functional Hydrobia ulvae Laver spire shell
Important functional Littorina littorea Common periwinkle
Important other Cerastoderma edule Common cockle
Important other Arenicola marina Blow lug


Zostera noltii stabilizes the substratum, promotes sedimentation of particulates and detritus, and provides substratum for epiphytes and refugia for other species. It is also a significant source of primary production and detritus. Hydrobia ulvae and Littorina littorea have been considered important functional species because they graze periphyton and epiphytes, which could otherwise reduce the light and nutrients available for Zostera noltii and may smother the seagrass. For example, Philippart (1995a, b) estimated that periphyton could reduce light incident on Zostera noltii blades by 10 -90% reducing the time available for net photosynthesis in the seagrass by 2-80%. She estimated the Hydrobia ulvae population was able to ingest 25 -100% of the standing crop of periphyton and microphytobenthos on a daily basis. She also suggested that the potential decline in Zostera noltii beds in the Wadden Sea due to shading by epiphytes had been offset by an increase in the Hydrobia ulvae population in the 1970s-1980s and noted that a previous decline in the mudsnail population in the early 1970s coincided with abnormally high fouling of the leaves of seagrass (Philippart, 1995a & b). Arenicola marina has been included as 'important other', partly to represent the sensitivity of polychaete species and because it has been shown to compete with Zostera noltii, potentially limiting the distribution and recruitment of Zostera noltii (Philippart, 1994a). Cerastoderma edule has been included as important other to represent the sensitivity of the bivalves.

Additional information

The MNCR survey recorded 185 species from this biotope. Asmus & Asmus (2000b, Table 1 and Figure 8) review species diversity in intertidal seagrass beds in the Sylt-Rømø. Davison & Hughes (1998) list representative and characteristic species of Zostera sp. beds. Species lists for major eelgrass beds are available for the Helford Passage (Sutton & Tompsett, 2000). Species lists are likely to underestimate the total number of species present, especially with respect to microalgal epiphytes, bacteria and meiofauna. Asmus & Asmus (2000b) noted that ostracods and copepods and fish were under estimated. However, many of the species found in intertidal seagrass beds are not specific to the community (Asmus & Asmus, 2000b). Therefore, although intertidal seagrass beds make a major contribution to primary and secondary production within the intertidal sedimentary ecosystem, loss of the seagrass beds would have a minor effect on species richness, especially with respect to the infaunal community (Asmus & Asmus, 2000b).

This review can be cited as follows:

Tyler-Walters, H. & Wilding, C.M. 2008. Zostera noltii beds in upper to mid shore muddy sand. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 29/11/2015]. Available from: <>