Other physical factors
Temperature and Climate
The effects of emersion, wave-action and topography can be modified by
other important factors. The geographical situation of any shore will determine the
species which are available to colonise it, the degree of exposure to wave action and the
stresses which organisms face at higher shore levels.
Temperature and Climate
In general terms, water temperature is the most important factor determining the
distribution of marine organisms (Lüning and Asmus, 1991). Air temperatures are
also important for littoral species.
Effects on limits of distribution
Many species reach the northern or southern limits of their
distributions around the UK (Lewis, 1964). These limits can fluctuate, responding to
fluctuations in climate (Crisp, 1964; Southward et al, 1995). Climate also affects
the relative competitive abilities of species. This is particularly well illustrated by
the barnacles Semibalanus balanoides, Chthamalus stellatus and C.
montagui. On shores on the West coast of Scotland, C. stellatus and C.
montagui are restricted to high shores as S. balanoides, the northern
species, is competitively superior at these latitudes (Connell, 1961a,b). Further south in
the UK, the two genera coexist in the mid shore (Crisp et al., 1981).
Degree of Disturbance
Climate can also affect the degree of disturbance suffered by shore
communities. The extent of damage inflicted by water-borne debris increases as wave
exposure and storms become more severe. At very high latitudes, where sea water freezes,
ice scour can cause massive mortality of encrusting species during the winter months,
though this rarely affects UK shores. Occasional hot summers can cause a disturbance on
British rocky shores (e.g. Hawkins and Hartnoll, 1985)
The supply of particulate organic matter to shores will depend on the
local hydrodynamic regime, especially in relation to local processes of erosion and
fluvial input. More of this material will arrive at the shore by advection when the
prevailing wind blows towards the shore. Species tolerant to low salinities are able to
colonise shores in estuaries and bays with substantial freshwater inflow. Offshore events
help structure rocky shore communities not only by affecting levels of wave exposure and
food supply but also by affecting the survival and onshore transport of larvae.