Glare Island Survey — Marine Algae. 15 59 



Corallina, Gelidium, and Cladostephus, and having a tendency to approach 

 the Rhodoclwrton floridulum, association. The presence of Cladostephus 

 spongiosus together with Corallina officinalis is very characteristic of this 

 vegetation, and hence the name selected. 



The community in question is essentially one of flat, sheltered rocks, 

 avoiding the clean rocks and turbulent conditions enjoyed by Laurencia, but 

 thriving with more slope and slightly more exposure than R. floridulum. It 

 occupies the same bathymetric range as Laurencia pinnatiflda, and though 

 capable of growing in the shallow sub-littoral region, it more often gives place 

 to Gigartina or Laminaria. At Portlea it is intimately associated with 

 Bhodochorton, but the two communities are usually sharply defined, and 

 distinguishable at once to the eye, as well as to the tread. 



Though both Corallina and Cladostephus are rock-attached, a thin layer 

 of sand is often found on the surface of the substratum. Corallina, under 

 the conditions obtaining, is short and more or less erect, its stiff branches 

 easily retaining sand and fine debris, so much so that the presence of 

 blackened sand and particles of decayed matter is almost characteristic of the 

 community. At the same time it is not truly psammophilous. A vegetation 

 of the same natm-e (though differing slightly floristically) has already been 

 described by me in connexion with the growth of Ulva, and the origin of the 

 blackened sand is explained ('11, pp. 124 and 128). 



The Corallina-Cladostephus sward is seldom so extensive as that of 

 Rhodoclwrton floridulum, being patchy, and only occasionally forming broad 

 belts. Gelidium aculeatum is sometimes present in quantity, and C. squamata 

 is common, especially in the more open regions. A very heavy epiphytic 

 vegetation exists, of which Enteromorpha clathrata, Ulva, Leathesia, 

 Ceramium fldbelligerum, and C. rubram are the most abundant. Callithamnion 

 Ifookeri also is found in summer on Cladostephus. In addition to the above, 

 a large number of sporelings occur. These succeed better on this vegetation 

 than on Rhodochorton (where sporelings are exceedingly numerous) ; and 

 though the plants do not attain their maximum size, they usually fruit, and 

 are sufficiently large to give distinct patches of colour. Much Cladophora 

 sericea and C. albida is present in spring ; Cerammm rubruni in various forms 

 is abundant in summer; whilst in October (1910) a form of Enteromorpha 

 clathrata was very conspicuous. In summer Ulva also is present in great 

 quantity, as has already been pointed out (Cotton '11, p. 128), being saxicolous 

 or epiphytic. 



On Clare Island the association occurs on a small scale at Portlea and 

 Kinnacorra ; and on the mainland at many spots in the outer part of Clew 

 Bay (Eoonah, Louisburgh, Mulranny). A similar vegetation occurs on the 



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