Localised short term fluctuations in seawater temperature, resulting from heat loss or gain to the air or the substratum, can occur in the shallow surface layer in inshore water. CFT communities are largely insulated from such transient influences by their depth, and in many cases also by their prevalence in high energy systems which ensure vertical mixing of these variable surface waters with the more stable deeper layers. Seasonal shallow thermoclines may form, particularly in sheltered areas such as sea lochs, and extend down to 15m. Some animals such as the brachiopods Crania and Terebratulina seem restricted to below this thermocline (Hiscock, 1985).

The permanent thermocline represents a more substantial effect of depth on temperature. However, typical CFT communities within SACs will be located well above this, which is generally at around 200 m, and rarely above 80 m. Hence they will experience the annual temperature fluctuation of about 8° C characteristic of British coastal waters. There are deeper water circalittoral rock biotopes which occur beneath the thermocline and which are temperature sensitive - such as the Lophelia reefs. However, these will not occur within the limits of the proposed SACs. There have been suggestions that deeper water temperature-sensitive communities can be discriminated below 40 m off the Glénan Archipelago (Castric-Fey et al., 1973) and off Galway (Könneker, 1977).

The most obvious effects of temperature result from the geographical variation of seawater temperature, which generally decreases from the south-west to the north-east across the British Isles. Summer surface temperatures range from around 16-18° C in the south to 12-13° C in the north, with corresponding winter ranges of 9-10° C and 4-5° C respectively. These geographical variations of temperature are reflected in the distribution of important CFT species, such as the soft coral Alcyonium glomeratum, and the sea fan Eunicella verrucosa (Appendix 4, Figure 14b). These are both southern species, and limited tolerance of cold determines the northern limits of their distribution. On the other hand the northern sea fan Swiftia pallida (Appendix 4, Figure 14c) has a more northerly distribution. Similarly some JNCC biotopes can be geographically restricted because they are characterised by temperature sensitive species. Thus the 'erect sponges, Eunicella verrucosa and Pentapora foliacea on slightly tide-swept moderately exposed circalittoral rock' biotope is confined to the south west. Geographical distribution patterns for biotopes and species are both discussed in detail in section III.E.

Anything affecting the annual temperature regime can affect the abundance and distribution of temperature-sensitive species. The possible, but currently unquantifiable, effects of long-term global warming are touched on in section IV.A. There are however shorter term cyclical temperature fluctuations operating in the north Atlantic, such as those associated with the so called North Atlantic Oscillation (NAO), with a period of 7-8 years (Maximov et al., 1972). A variety of benthic populations have been demonstrated to co-fluctuate in abundance accordingly (Gray & Christie, 1983), and such cyclic fluctuations are recorded from typical rocky circalittoral species such as Ciona intestinalis (Lundälv, 1985) and Echinus esculentus, Asterias rubens and Ascidia mentula (Lundälv & Christie, 1986). The management implication is that such cycles must be discriminated from anthropogenic changes, and that areas may need to be compared and only "departures from a common pattern may indicate local effects of pollutants" (Gray & Christie, 1983). This may be facilitated if similar formats of monitoring are undertaken in adjacent SACs.

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