Habitat requirements

Habitat factor Range of conditions
Salinity Full, Variable, Reduced / low

Salinity in pools and crevices in the littoral zone can vary considerably with evaporation and dilution by rain.

Wave exposure Sheltered, Very sheltered, Extremely sheltered

The structure of ecological communities on rocky shores is affected by a horizontal gradient of exposure to wave action, from sheltered bays to exposed headlands. The degree of wave action on a particular shore is determined by the aspect of prevailing winds coupled with the ‘fetch’: the distance over which winds blow. Exposure to wave action affects the distribution of species, according to their tolerances. With decreasing exposure the risk of dislodgement and physical damage decreases, resulting in a greater preponderance of fragile species. Morphological differences can be observed between members of the same species from wave-exposed and sheltered sites. For example, dogwhelks from wave-exposed shores have thinner shells with larger apertures than those from sheltered shores.

Substratum Bedrock; boulders; cobbles; pebbles; mixed substrata on sand and mud.

Hard rocks provide a more secure anchorage for large plants and animals such as fucoids and limpets. Sheltered rocky shores can consist mainly of bedrock or they may be a mixture of bedrock and boulders, cobbles or pebbles intermixed with sediment..

Height band Strandline, Upper shore, Mid shore, Lower shore
Zone Eulittoral
Temperature At the interface between land and water, species spend part of their time immersed in the sea and part of their time in contact with the air, with a vertical gradient of emersion up the shore. Air temperatures commonly fluctuate by 10 to 20oC in a 24-hour period whereas sea temperatures usually fluctuate by less than 10oC in a year. Intertidal areas are also exposed to the rigors of sunlight at low water especially when low water spring tides occur around midday.
Tidal range Tidal ranges from 0.5 m to 12 m in the British Isles. Greater tidal ranges result in more extensive littoral zones.
Desiccation In temperate zones, the risk of desiccation due to heat and low humidity is highly significant. The ability of species to tolerate desiccation will effect community structure, as will wave exposure, which can modify the extent of the vertical gradient. The elevation in the zonation pattern observed on exposed shores will not be found on sheltered shores, as ‘wave splash’ will be minimum.
Slope/shore topography Rock type influences the slope and topographical complexity of the shore, and slope determines the area available for littoral species. Barnacles and limpets are successful on steep shores, while mussels and seaweeds are more common on gently- sloping or horizontal shores.

Next Section                     References