CHAPTER V 



Some Methods of Attack and Defence among Shore 



Animals 



In the foregoing chapter we have discussed the methods 

 by which shore animals cope with some of the chief problems 

 offered by their environment. We have now to deal with 

 another aspect of the struggle for existence on the sea-shore, 

 namely the conflict between the animals themselves. It is 

 safe to say that in no other area are the weapons and strata- 

 gems of offensive and defensive warfare so varied in character 

 as on the sea-shore. This is the logical outcome of the many 

 advantages presented by this particular habitat : light, 

 aeration, abundance of plant-food, the presence of a sub- 

 stratum, etc. Moreover, the same comparative isolation of 

 shore areas due to the shallow waters (and the consequent 

 importance of even low physical barriers) which has favoured 

 the evolution of new forms has also stimulated the production 

 of new methods of sustaining the conflict. 



The methods of attack and defence with which we are 

 to deal are essentially those employed in the struggle for 

 food among animals of different kinds, e.g. carnivores and 

 herbivores. There is, however, a type of struggle which, 

 having a somewhat different biological significance from that 

 of attack and defence as generally understood, demands 

 separate consideration. This is the tendency, an outcome 

 of crowded shore conditions, for many animals to lodge on 

 the bodies of others. We are not dealing here with cases 

 of parasitism nor of commensalism (properly so called), 

 but more especially with those of sessile forms : hydroids, 

 polyzoa, barnacles, etc., settUng on the bodies of other 



85 



