CHARACTERISTICS OF ASSOCIATIONS 



their inter-relationships being as represented in the accom- 

 panying diagram : 



SHALLOW SEA OPEN J£A 



Pe/adic Realm 



too FA THOMS 

 1^ APPROK LIMIT of WAVE-ACTION 



5, And of PLANT LIFE 

 2. 



200 FATHOMS 



ZOOO FATHOM 5 



Deep 5ea 



(Abyssal Tied In) 



OCEAN BA5IN 



Fig. I. — Marine zones (after Lull). 

 Strand or Tidal Zone. — This area, to the study of which 

 the present book is devoted, is the narrow strip of territory 

 between the high and low water-mark of spring tides. It 

 is remarkable for its situation at the junction of sea and land, 

 a region of unceasing activity and of extraordinarily fluctuat- 

 ing conditions. Among other characters which distinguish 

 it are the presence of a substratum, abundance of light and 

 of aeration. Plant life (in the form of alg^) is frequently 

 very important on the shore and presents a certain analogy 

 with land conditions in contrast to the purely marine con- 

 ditions existing beyond the littoral zone, where plant life 

 gradually dies out as the depth of water increases. Fresh- 

 water drainage from the land frequently has considerable 



