Biodiversity & Conservation

Hydroids, ephemeral seaweeds and Littorina littorea in shallow eulittoral mixed substrata pools


Hydroids, ephemeral seaweeds and <i>%Littorina littorea%</i> in shallow eulittoral mixed substrata pools
Distribution map

LR.LR.Rkp.H recorded (dark blue bullet) and expected (light blue bullet) distribution in Britain and Ireland (see below)

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
Important characterizing Obelia longissima A hydroid
Important characterizing Littorina littorea Common periwinkle
Important characterizing Ulva intestinalis Gut weed
Important other Mytilus edulis Common mussel
Important other Semibalanus balanoides An acorn barnacle


The hydroid Obelia longissima is particularly characteristic to this biotope. The common periwinkle is part of the biotope name and has therefore also been listed as an important characterizing species. Ulva intestinalis, although not a characterizing species per se, is representative of other ephemeral green algae that may be found in LR.H. It also provides a food source for the common periwinkle. The common mussel Mytilus edulis has been included as another important species since it was found in almost all records of the biotope, often in abundance, and mussel patches may provide some stability to this otherwise unstable and transient biotope. The acorn barnacle Semibalanus balanoides is likely to be found attached to stones and shells. It has been listed as important 'other' since it may be common is some LR.H pools.

Additional information

The MNCR reported 129 species from this biotope, although not all species occur in all examples of the biotope (JNCC, 1999).

This review can be cited as follows:

Marshall, C.E. 2005. Hydroids, ephemeral seaweeds and Littorina littorea in shallow eulittoral mixed substrata pools. 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: <>