312 MARINE ECOLOGY 



There are some features of particular interest from the individual 

 localities which may suitably be discussed at this stage. Anand 

 (1937) in his study of the Dover cliffs carried out some experiments 

 with a view to determining the nature of the controlling factors. 

 The greatest attention was given to the water relations, and it was 

 pointed out that the water content of the algal covering depends on 



(a) the supply of water, e.g. tides, spray, rainfall, humidity, 

 moisture of the substrate ; 



(b) the water loss due to various causes, e.g. evaporation, drain- 

 age and capillary attraction of neighbouring belts, the latter being 

 effective up to a distance of 40 cm. ; 



(c) the physical nature of the algal covering, e.g. whether delicate 

 plants, leathery plants or gelatinous plants, whilst the quantity of 

 water retained will also depend upon the thickness of the algal 

 mat. 



It was found that the Enteromorpha mat lost 25 % of its moisture 

 in the first 3 hours of exposure, whilst the Chrysophyceae belt lost 

 18-4%. The relative loss by evaporation of Enteromorpha and 

 Chrysophyceae mats is seen in fig. 195 A, whilst the corresponding 

 loss due to drainage is shown in fig. 195 B, the two sets of measure- 

 ments being obtained by the simple but ingenious method of 

 weighing portions of the mat cut out so that they fit into water- 

 proof paper dishes which could be put back into position on the 

 shore. The differences in loss for both evaporation and drainage are 

 due to the gelatinous nature of the Chrysophyceae belt, and this 

 result is obtained in spite of the fact that the evaporating power of 

 the air opposite the latter belt is 1-41 as compared to i-i opposite 

 the Enteromorpha belt, the evaporating power of the Fucus belt 

 being taken as unity. 



Similarly, the concentration of salt in the Chrysophyceae belt, 

 which shows little variation, can be compared with that of the 

 Enteromorpha belt which varies considerably with level and length 

 of time after fall of the tide. The day temperature of the belts only 

 responds to changes of air temperature in summer, and then it is 

 always less than that of the air although the seasonal range is greater. 

 The temperature range is greatest in the Fucus and least in the 

 Chrysophyceae belt as the latter retains more moisture. If, 

 however, the period of insolation is at all long, as may well happen 



