44 THE BIOLOGY OF THE SEA-SHORE 



difficulties occur in dealing with wide sandy and muddy 

 areas which are largely barren of plant life, in which case the 

 name of a dominant animal species must be used. 



The first zone encountered is either the Salicornetum 

 (typical plant Salicornia, the Salt-wort) of muddy or sandy 

 coasts, or the Enteromorpha Association. The latter, how- 

 ever, varies in position with regard to the manner in which 

 fresh water appears along the shore-line. At times it forms 

 a bright green band near high-water mark, but by the end 

 of summer much of it may have been killed by drought, and 

 then appears as a band of white dead tissue (Cotton, 19 12). 

 The succeeding Fucaceae Association, typical of exposed 

 coasts, is of especial ecological value and affords a good deal 

 of shelter for other forms. Cotton (op. cit.) gives the typical 

 sequence of species from above downwards, as follows : 

 I. Pelvetia canaliculata. 2. Fmcw^ ^pz'mfe (disappears under 

 very sheltered conditions). 3. Ascophyllum nodosum (needs 

 a moderate amount of shelter). 4. Fticus vesiculosus (cannot 

 stand exposure). ^. F.serratus. 6. F.ceranoides {admixture 

 of fresh water a necessity). Many epiphytic species take 

 advantage of the size of, and shelter afforded by, these 

 Fucoids which, when present in abundance, impart a most 

 marked aspect to the shore, obscuring the rocks with their 

 masses during low water, and waving in dense groves buoyed 

 up by their bladders during the tidal period (cf. Plate VHI). 



The Fucus Associations of Achil Sound showed the 

 following widths : 



