﻿Study of the Animal Ecology of the Shore. 227 



complexity of environmental relations. In each subdivision 

 of the beach — zones, fresh-water areas, and positions, we 

 must study (1) the correlation of the structure and behaviour 

 of its inhabitants with the physical peculiarities of the 

 division, and (2) the interrelations existing between the 

 species found in it. 



But there are certain fluctuating environmental conditions 

 which will affect the beach as a v/hole, and be felt by all its 

 inhabitants. We must make allowance in our scheme for 

 the study of their effects. 



The chief of these changing conditions is undoubtedly the 

 state of the tide. What we might call the statical relations 

 of shore animals to depth are best considered by dividing up 

 the beach into zones, as we have already proposed to do ; 

 but it is evident that the activities of the inhabitants in each 

 zone are largely influenced by the state of the tide. The tide 

 makes all the difference for some species between activity 

 and quiescence or even latent life. For instance, many 

 species take shelter in holes and corners when the tide is 

 out, and travel freely when covered ; Littorina rudis is often 

 found quite above ordinary high-water mark, and according 

 to Bohn's observations ^ it subsists in a state of suspended 

 animation from one spring tide to another. It will be 

 necessary then to note the state of the tide when collecting 

 from the various positions. 



It might also be well to study the variations associated 

 with the alternation of night and day. Another influence 

 which seems to have a certain effect upon the intimate 

 distribution and the activities of shore animals is the degree 

 of humidity of the air, especially when this affects in a 

 marked degree the surface of the stones and weeds, making 

 them moist or dry. For instance, we have observed that 

 Littorina rudis, on the higher part of the beach, comes out 

 on the tops of stones in greater numbers in damp weather 

 than in dry. Along with this the other weather conditions 

 should be considered — of rain, sunshine, temperature, 

 barometric pressure, and direction and force of the wind. 

 The effect of storms upon the shore fauna is often quite 



1 C.R. Acad. Sci., cxxxix. (1904), pp. 610, 611. 



