Clare [stand Survey — Marine Algae. 15 63 



(a) Littoral Region. 

 Rhizoclonium riparium community. 



The only community found on pure sand in our area is that of Rhizoclonium, 

 though for this also a small amount of binding material is advantageous. 

 The vegetation is found immediately below high-water line, and is 

 occasionally very conspicuous, specially in spring and summer. At Mulraimy, 

 where the shore is unusually Hat, Rhizoclonium covers extensive areas, patches 

 an acre in extent having been noted. 1 



The underlying sand (or sandy-mud) is for the most part firm, often 

 bound together by Microcoleus, but in other spots it is loose and apt to 

 become dry. In either case Rhizoclonium lies as a loose covering, thus 

 feeling the effect of wind and tide, often being more or less buried. In some 

 localities the upper part of the association is during neap-tides not wetted at 

 all, and in this way differs from the somewhat similar filamentous vegetation 

 which lies on wet mud, e.g. on the Vaucheria Thvretii association in Achill 

 Sound (p. 64). Rhizoclonium riparium is usually a pure dominant, but 

 amongst it (especially in the damper parts ?) occur Enteromorpha prolifera, 

 E. clathrata var., and Cladophora fracta. The blue-green species, so common 

 in the corresponding association on the salt-marsh, are absent. 



A very similar type of growth to that described above has been noted in 

 Poole Harbour, and on a small scale near the mouth of the River Bann. (See 

 also salt-marsh formation, p. 79.) 



Microcoleus chthonoplastes association. 



Of the sand- and mud-binding algae one of the most important is Micro- 

 coleus chthonoplastes, a microscopic species of world-wide distribution. The 

 plants are often completely hidden in the substratum ; but their presence 

 can be detected by the way in' which the soil holds together, and peels off' in 

 crusts, when lifted up. Though Microcoleus has not been previously recorded 

 as forming an association as such, the plant-community has as a fact been 

 long known, and for a description one cannot do better than quote Gomont's 

 note in his revision of the Oscillarieae ('09, p. 92) : — 



" Le Microcoleus chthonoplastes se rencontre quelquefois a letat de filaments 

 isoles melanges a d'autres Algues, . . . mais il occupe aussi a lui seul de 

 vastes etendues sur les cotes marecageuses ou sablonneuses. II joue un role 

 des plus utiles dans l'exploitation des marais salants en recouvrant le fond 

 des bassins ou oeillets d'un tapis compact qui permet d'enlever les cristaux 



1 The flatness of the shore at this spot may be judged from the fact that the Pelvetia zone, which 

 is only about 1 foot deep, is in places over 80 yards wide. 



