THE BASIC ZONATION 



313 



in the summer months, then the Chrysophyceae mats frequently 

 become cracked and fall off. 



Light, currents and temperature are the chief factors determin- 

 ing the incidence of cave vegetation, winding caves showing the 

 influence of light best. Lack of sunlight stops Fiicus from invading 

 these areas and when the light intensity is low the Chrysophyceae 

 also are not able to develop satisfactorily. There is no algal growth 



% 



WATEK 

 LOSS 

 35 



LOSS 



90 r 



1 2 3 



Time in hours 



2 3 4 



Time in hours 



Fig. 193. A, water loss from samples of Enteromorpha and Chrysophyceae belts 

 when exposed in their original position on the cliff face. B, water loss during 

 drainage in nature from different levels in the Enteromorpha and Chrysophyceae 

 belts during successive hours in winter. E1-E3, C1-C3 = successive levels. Water 

 loss in A and B expressed as % of that originally present. (After Anand.) 



in long and relatively straight caves beyond a distance of about 

 15-5 m. from the entrance where the light intensity has been reduced 

 to about 1-8% of the Hght outside. 



A somewhat different ecological approach was adopted by 

 Colman (1933) at Wembury. He carried out statistical analyses, 

 and these showed that so far as the fauna and flora were concerned 

 there are probably three critical levels : 



(a) Between mean and extreme low-water marks of spring tides 



