Habitat requirements

Habitat factor Range of conditions
Salinity Full, although salinity in pools and crevices in the littoral zone can vary considerably with evaporation and dilution by rain.
Wave exposure Extremely exposed, Very exposed, Exposed

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. Shores with a long fetch can have strong wave action because the wind has a greater distance to generate the height of waves. Such shores may also receive swell on windless days, resulting from distant storms. Exposure to wave action affects the distribution of species, according to their tolerances. Increased exposure favours certain sessile, filter -feeding species. At the same time, increasing exposure carries an increased risk of dislodgement and physical damage, limiting the range of susceptible and physically fragile species.


Bedrock; large boulders.

Hard rocks provide a more secure anchorage for large plants and animals such as fucoids and limpets.

Height band 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, or at least splashed by its spray, 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 will also be 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.
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. As wave action increases, so does the amount of spray produced. Waves with greater amplitude break at higher shore levels, showering still higher areas with spray. At very exposed sites, shore levels well above the highest tide level may regularly be wetted by the action of waves. It is not uncommon to find high shore species many tens of meters above the theoretical tidal limit on very exposed cliffs (Lewis 1964).
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