Biodiversity & Conservation

Ascophyllum nodosum, sponges and ascidians on tide-swept mid eulittoral rock


<i>%Ascophyllum nodosum%</i>, sponges and ascidians on tide-swept mid eulittoral rock
Distribution map

LR.SLR.F.Asc.T recorded (dark blue bullet) and expected (light blue bullet) distribution in Britain and Ireland (see below)

  • UK_BAP

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.

Community Importance Species name Common Name
Key Structuring Ascophyllum nodosum Knotted wrack
Important characterizing Halichondria panicea Breadcrumb sponge
Important characterizing Ascidiella scabra A sea squirt
Important other Littorina obtusata Common flat periwinkle
Important other Fucus serratus Toothed wrack
Important other Fucus vesiculosus Bladder wrack
Important other Patella vulgata Common limpet
Important other Chondrus crispus Carrageen


Ascophyllum nodosum characterizes this biotope and its dense canopy provides a substratum for a variety of epiphytes in addition to protecting the underlying flora and fauna from desiccation and insolation. It has been listed the key structural species since its removal would destroy the biotope. Sponges and ascidians also characterize this biotope and Halichondria panicea and Ascidiella scabra have been included as representatives of these two groups, although there is a diverse suspension feeding community. Ascidiella scabra is not as frequent in occurrence as Dendrodoa grossularia; however, more information was available for the former in terms of sensitivity assessment. Given the longevity of the knotted wrack and the sheltered nature of the habitat, the grazing activity of the flat periwinkle Littorina obtusata is likely to be the only significant factor affecting the structure of the plant's population. Similarly, Patella vulgata is likely to maintain a steady state in terms of the ratio of bare rock, encrusting algae and red foliose seaweeds. For these reasons, the two grazers have been included as 'other' important species. The fucoids Fucus serratus and Fucus vesiculosus may also be present as part of the canopy layer. Although they are not characterizing species, they provide substratum for various epiphytes, especially the hydroids Dynamena pumila and Clava multicornis and, accordingly, have been included as other important species. The red algae Chondrus crispus, although not the most abundant red algae or most frequently associated with this biotope, has been included to represent the diverse range of red seaweeds that occur in this biotope. Insufficient information on the most abundant red algal species, Polysiphonia lanosa, meant that this species was not suitable for assessing the sensitivity of other red algae.

Additional information

This review can be cited as follows:

Marshall, C.E. 2005. Ascophyllum nodosum, sponges and ascidians on tide-swept mid eulittoral rock. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 30/11/2015]. Available from: <>