ECOLOGY OF ROCKY COASTS 333 



divided into (a) wash zone, which is the height the actual wave 

 washes up the rock face, (b) the splash zone, which is represented 

 by actual splash from the wave, (c) the spray zone. On exposed 

 coasts in the Isle of Man the wash zone extends down the whole 

 shore (Fig. 192) and this is probably true in other parts, e.g. 

 Pacific shores of America, Tasman Sea shores of New Zealand. 

 The splash zone (b) is generally only a few feet but the spray zone 

 (c) may be considerable. On the West Coast of New Zealand ht- 

 torinids occur up to 40 ft. above the highest spring tides, and the 

 spray from the giant waves can be seen drifting in nearly every day 

 of the year. It is likely, however, that the size and growth of algal 

 organisms in such elevated zones is not only due to the waves, but 

 is also dependent upon moist air conditions that keep them damp 

 during low tide periods. 



It might be thought that the bathymetric levels of the different 

 belts on the shores would be very uniform throughout a region be- 

 cause it could be argued that the controlling factors would be uni- 

 form. SuflScient work has been carried out now to show that this 

 idea is not correct. In Great Britain the bathymetric levels of Fucus 

 vesiculosus and F. serratus vary from place to place (Knight and 

 Parke, 1950). In New Zealand the belts of the major dominants 

 show considerable variation, even after allowance has been made 

 for splash elevation. Work over a considerable range of coast-Une 

 has also demonstrated that change of latitude may exert an in- 

 fluence upon the belts. Gislen (1943) has shown that on both sides 

 of the Pacific the belts of brown algae tend to emerge with increase 

 in latitude. Knight and Parke (loc. cit.) have shown the same thing 

 to hold true for Fucus serratus though work in New Zealand (Tre- 

 varthen, 1954) has shown that Hormosira occupies significandy 

 lower levels as one goes southward. 



We may now consider the regional variants of Stephenson's basic 

 zonation. In the North Sea and on the colder Adantic shores of 

 Europe the supra-httoral fringe is occupied by species of Lit torina^ 

 with which are commonly associated belts of Porphyra umbilicalis 

 and Pelvetia canaliculata. The last two species are essentially 

 characteristic of colder waters. The mid-littoral is characterized by 

 the presence of barnacles, though they do not necessarily occupy 

 the full vertical range. On very exposed coasts these frequendy 



1 Where the rock surface is extensive there is often a 'black' lichen belt com- 

 posed of Lichina confinis and Verrucaria maura above the Littorina. 



