| 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 |
Moderately 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. |
| Substratum |
Bedrock; boulders; cobbles Hard rocks provide a more secure
anchorage for large plants and animals such as fucoids and limpets. |
| 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, 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. 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. 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. |
| 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. |
