Clare Island Survey — Marine Algae. 15 51 



Hilderibrandtia-Verrucaria Association . 

 Brief notes may be added to previous remarks with regard to this 

 association (p. 19). On the sheltered shores of Clew Bay the same species 

 are present, especially on boulders and smooth rocks. Where these are absent 

 a discontinuous growth on stones and pebbles occurs, and in such spots 

 Hildenbrandtia is joined near low- water mark by Porphyrodiscus simulans and 

 Rhododermis elegans (plants hardly distinguishable in the field), and also by 

 Ralfsia clavata. H. prototypes itself, moreover, appears to extend to the 

 sub-littoral region (cf. p. 20). The difficulties of obtaining satisfactory 

 material and of distinguishing the species when collecting, make it no easy 

 matter to gain a true idea of the different societies. It is certain, however, 

 that in these localities the Ralfsia clavata vegetation is one with the 

 Hildenbrandtia association, and that it forms a part of it. It is further 

 evident that a vegetation composed of soft encrusting algae and lichens 

 extends uninterruptedly from high-water mark down to the Lithoderma 

 association of 5-8 fathoms. The details require working out, but roughly 

 the principal species form zones as follows : — 



Hildenbrandtia prototypus (upper littoral). 

 Verrucaria mucosa (middle littoral). 

 Ealfsia clavata (lower littoral). 

 Cruoriopsis Dubyi (shallow sub-littoral). 

 Lithoderma fatiscens ? (shallow sub-littoral). 



Fucaceae Association (sheltered). 



The growth of Fucaceae on flat sheltered shores is exceedingly luxuriant, 

 and often forms a conspicuous feature of the landscape. The indispensable 

 factor is good anchorage. ,On flat shores, where wave-action is slight stones 

 are sufficient to supply this necessity, but where rocks and stones are wanting 

 Fuci are conspicuous by their absence. The association was studied especially 

 in Achill Sound, the north part towards Inish biggie and Bellacragher Bay 

 having been examined, as well as the southern portion towards Achillbeg. 

 As far as was seen the Fucus growth in Clew Bay is of a precisely similar 

 nature. 



The association is composed of the usual five species in their normal 

 sequence (see p. 23), and where fresh-water streams occur, the sixth species, 

 F. ceranoides, invariably appears. In some places the zones are fairly sharply 

 defined ; in others they are much less distinct, and each zone overlaps the 

 next. A certain amount of irregularity exists too as to the order in which 

 Aacophylluin and F. vesicalosus occur. The former usually commences above 



G2 



