SOME BIOLOGICAL EFFECTS OF 

 THE TIDES 



By F. W. FLATTELY 



Lecturer in Zoology, Armstrong College, Newcastle-on-Tyne 



Fringing every continental land-mass is an area, for the 

 most part very narrow, which belongs properly neither to land 

 nor sea, but is the disputed province of both these realms. 

 Although, on a superficial view, it is by no means favourable 

 to life, the tidal zone turns out, on closer examination, to be 

 one of the richest in variety of animal life on the surface of 

 the globe. 



Every distinct haunt of life brings its own special problems 

 to be solved by the animals that live there, but the problems 

 which confront shore animals are particularly urgent. The 

 factor which gives the seashore its peculiar ecological character, 

 or rather, from the ecological point of view, makes this area, 

 is the tides. An examination of the tides from the biological 

 aspect shows that they have had many important consequences, 

 not only for the present life of the sea-shore, but also — it seems 

 not too much to say — for life in general. 



Whether life began in the open sea or in the shallow waters 

 of the littoral or in fresh-water pools scientists have not been 

 able to decide. Nevertheless, one thing is certain, namely, 

 that if life did not originate in the tidal zone nor in the area 

 immediately below it, as some still think possible, then life 

 was not very long in reaching there. It is unnecessary to 

 adduce special proof of this statement : the vast number of 

 invertebrate animals that frequent, or have frequented, or have 

 relatives on the shore, from sponges, through coelenterates, 

 echinoderms, worms, crustaceans, and molluscs up to ascidians, 

 allow of no other conclusion. In its earlier youth, then, life 

 served an apprenticeship to the tides, and it is probably not too 

 much to say that life is continuing to show the effects. That 

 is what was meant in speaking just now of demonstrating the 

 consequences of the tides to life in general. That is what 

 biologists intend to express when they speak of the shore as 

 the school wherein many of the most important lessons of life 

 were learnt. 



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