MARINE ECOLOGY 



307 



about the factors that cause removal of algae from rocks. Statistical 

 analyses of drift show that the majority of Laminariaceae are torn 

 in their entirety from off the rocks, so that removal in their case 

 cannot be due to epiphytes or to the boring of the stipe by the 

 mollusc, Patina pelluctda, and as they usually grow beneath low-tide 

 mark surf action is also removed as a possible destructive factor. 

 It may be that the continual swell and strong currents finally bring 

 about their destruction. In the case of smaller algae, however, the 

 weight and resistance of an excessive epiphytic flora brings about 

 the uprooting of the host plant. This, and numerous other problems, 

 await the attention of future investigators. 



Table XII contains in a summarized form the principal com- 

 munities that have been recognized around the coasts of Great 

 Britain. It is not proposed that any of these should be described in 

 detail, but it is hoped that the outline provided by this table may be 

 a guide to students who visit any of these areas. One of the 

 principal characteristics of any rocky shore is the way in which the 

 different algae are distributed in zones or belts at the different 



f the British Isles 



Clare Island 

 (Ireland) 



ichina 



lldenbrandtia- Verrucaria 



rasiola stipita 

 nteromorpha intestinalis 



eltetia 



ucus spiralis 



ucus vesiculosus var. 



•vesiculosus 



ucus serratus 



Castletown 

 (I.O.M.) 



Pelvetia 



Fucus spiralis 

 Ascophylltim 



Fucus vesiculosus 

 Fucus serratus 



orphyra — 



angia- Lrospora- Ulothrix Porphyra- Urospora- 



Ulothrix 

 hodymenia Laurencia-Cladophora- 



Rhodochorton 

 aurencia-Gigartina Laurencia-Lomentaria 



allithamnion arbuscula 



emalion 



imanthalia 



orallina 



iminaria 

 icrusting algae 

 ystoseira 



scophyllum 



orallina-Lithothamnion 

 orallina-Cladostephus 

 hodochorton floriduluvi 



Himanthalia 



Laminaria 



Cromer 



(Chapman, J. Linn. Soc. 



{Bot.), 1917) 



Enteromorpha 

 Fucus platycarpus 



Fucus vesiculosus var. 



evesiculosus 

 Fucus serratus 



Fucus-Porphyra- 

 Enteromorpha 



Laurencia pinnatifida 



Hildenbrandtia- 

 Lithothamnion 



SUBLITTORAL 



Sheltered coasts 



Cumbrae 

 (Scotland) 



Enteromorpha intestinalis 



Porphyra- Urospora- 



Ulothrix 

 Pelvetia 

 Fucus spiralis 

 Ascophyllum 

 Fucus vesiculosus 

 Fucus serratus 



Laurencia 



Gigartina- Cladophora 

 Enteromorpha Lima 



Laminaria 



Enteromorpha-Cladophora- 

 Chordaria 



20-2 



