Clare Island Survey — Marine Algae. 15 73 



The Pebble-attached Association of Quiet Bays. 



This association represents a definite type of sub-littoral vegetation, which 

 is found on a soft bottom strewn with stones and pebbles. A very large 

 number of species go to form it, and they are for the most part characterized 

 by finely divided bushy fronds, though heavier and less bushy plants are found 

 on the larger stones and on the occasional pieces of rock. In some localities 

 almost every stone down to the smallest pebble bears a tuft of one or more 

 algae. The latter consist of members of the Green, Brown, and Red groups ; 

 and, though they vary considerably in different localities, the mixture of 

 colour is a marked feature and suggests comparison with Kjellmann's "Bunte 

 Formation." But both the constituents of that association, and the depth at 

 which it occurs, are different from those here described. The present vegeta- 

 tion corresponds rather to Borgesen's Stictyosiphon association and to Boye's 

 Dictyosiphon-Spermatochnus-Corallina formation, though Dictyosiphon is 

 not always present. The species are annual or short-lived, which in part 

 accounts for the varied aspect presented during the season. 



The association extends from just above low- water mark down into 3 or 

 4 fathoms. Its shallower regions may be studied in detail by wading at spring 

 tides, when the bushy fronds of Polysiphonia, Cladophora, Spermatochnus, 

 Dictyosiphon, etc., may be examined in situ. Dredging in deeper water 

 shows a very similar type of growth, though some species disappear and others 

 become more abundant. The colour of the red species improves with increased 

 depth. The association, which reaches its maximum development in May, is 

 well seen in many of the inner parts of Clew Bay, and has been studied specially 

 on the west side of Annagh Island, and, in a slightly modified form, in 

 Bellacragher Bay. In brackish localities an increase of Chlorophyceae is 

 apparent. 



As it occurs in Clew Bay the principal species are as follows : — 



(a) In spring — 



Enteromorpha clathrata. Lomentaria clavellosa. 



Cladophora Rudolphiana. Nitophyllum punctatum. 



Striaria attenuata. Polysiphonia urceolata. 



Stictyosiphon subarticulatus. P. elongata. 



Dictyotosiphon foeniculacea. P. nigrescens. 



Ectocarpus siliculosus. P. atro-rubescens. 



Pylaiella littoralis. Ceramium rubrum. 



Cystoclonium purpurascens. Grimthsia corallina. 

 Delesseria hypoglossum. 



K.l.A. PKOC, VOL. XXXI. K 15 



