Habitats of Molluscs: Rock Pools

When the tide goes out, pockets of water remain in hollows and depressions on rocky shores and platforms, and in deeper gullies with or without shading from an overhang. Rockpools vary according to height on the shore with respect to low water, the degree of wave exposure of the site, the salinity levels which will fluctuate either with evaporation or dilution from rainfall, and the morphology and dimensions of the pool itself.  A fifth factor which contributes to the variability is the biota the pool contains, especially the extent of coverage and species diversity of the macroalgae present.

Rock Pool

For this reason there is no definitive list which characterises rockpool mollusc communities.  Individuals, especially juveniles, of the mollusc species occurring on the surrounding substrate will be found within the pool.

Where a pool is sheltered and supports a rich and diverse assemblage of algae, especially the finer red algal species such as Ceramium spp. Corallina officinalis and Griffithsia spp., one can expect a wide range of small mollusc species including, subject to biogeographical constraints, the following:–

Remember: A rockpool at midshore level which is relatively extensive, stable and retains water throughout the tidal ebb is likely to contain species normally living at low water springs level and which would otherwise not tolerate midshore environmental conditions.