The slope of the substratum influences the CFT community because it affects the amount of incident light, and consequently the abundance of algal growth. There are various studies which contrast the abundance of algae on upward facing surfaces with the animal domination of nearly verticals and overhangs, on both natural substrata (Kitching et al., 1934; Forster, 1958, 1961; Hiscock, 1979a) and artificial panels (Withers & Thorp, 1977). This is clearly illustrated by Figure 7 which shows the biomass of plant and animal material on rocks of different slope at the same depth. The effect of this factor is that animal species which occur on rocks of all slopes at depths of 20 m or more become confined to steeper slopes, and then to verticals or overhangs, as the depth decreases: this is clearly shown by the soft coral Alcyonium digitatum in the Isle of Man (Hartnoll, 1975).

The other effect of slope is that is will affect the amount of silt settling out on the rock surface, and as discussed below certain species and communities are favoured or deterred by such silt settlement.

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