14 THE BIOLOGY OF THE SEA-SHORE 



towards low tide mark. And the same is true for the animals 

 associated with the weeds. 



Not only may we study the fauna of these zones or 

 horizons as a whole, but we may go further and study the 

 animals dwelling together among some marked algal or other 

 associations (such as a Fucus bed ; in a rock pool ; in an area 

 of sandy mud ; in a cockle or mussel bed, etc.). Interesting 

 results may be obtained by contrasting the fauna living on 

 and under stones, etc. King and Russell (1909) recognised 

 four chief positions in dealing with the fauna of a particular 

 bay, but the distinctions are capable of wider application. 

 These " positions " were (i) the upper surfaces of stones 

 (and rocks) ; (2) beneath stones (not embedded) ; (3) in 

 the substratum ; (4) on, or amongst, different kinds of 

 weeds (noting in the last case that the base and branches 

 of large algae will show typical associations of forms), 



Davenport (1903) grouped the fauna of another area in 

 a manner which is also of value (but more locally than 

 widely, as the groups are not always clearly defined), into 

 (i) sessile, (2) crawling, (3) burrowing, and (4) swimming 

 animals. This method of grouping is, however, physiologi- 

 cal rather than ecological. 



We may conclude these introductory remarks, intended 

 to be suggestive and not by any means exhaustive, by 

 summarising the chief features of an association. Within 

 any particular association a normal relation between its 

 members comes to exist. We shall find at the time we 

 examine it, a certain number of genera, species, and in- 

 dividuals, and these are more or less constant for each 

 association. Several members of any given genus may be 

 present, and one or more of these species may be abundant, 

 so much so as to be called dominanty while others are rare. 

 One member of an association may be large and prominent, 

 but relatively few in numbers ; while another is extremely 

 abundant, but microscopic in size. There will be a balance 

 between vegetable feeders, predatory species, and para- 

 sites ; though the predatory element may be largely external 

 to any given association (such as fish or bird). Any 



