MARINE ALGAL VEGETATION 135 



12. The Community of Corallina. 



The members of this community are Corallina officinalis, Gigar- 

 tina mamillosa, Chondrus crispus and Ahnfeltia plicata. These species 

 occur as a rule in luxuriant and more or less sharply defined as- 

 sociations, which very frequently occur together, and may therefore 

 be regarded as nearly related to each other. 



The fronds are branched, and their consistency is on the whole 

 firm because, as is known, Corallina is encrusted with calcium car- 

 bonate, Ahnfeltia is horny and Gigartina and Chondrus are car- 

 tilaginous. 



Gigartina and Corallina generally occur in a belt at the limit 

 of extreme low- water; in my diary I have always called this belt 

 the Gigartina-Corallina-be\t. Gigartina, however, extends higher up; 

 on exposed coasts right up to the Fuciis-beM, and even into that 

 as under- vegetation ; but, where Gigartina and Corallina meet, there 

 is most frequently a mixed belt. These associations belong to S. 

 and SW. Iceland. 



The Cora///na-association occurs most luxuriantly about low- 

 water mark. The species grows extremely socially, and entirely 

 covers depressions in the littoral zone which are more or less filled 

 with water. The association occurs on somewhat exposed and also 

 on very exposed coasts, but almost always in depressions surrounded 

 by rocks upon which the waves break; yet I have seen it, where 

 the exposure is but slight, covering the face of rocks below low- 

 water mark. Only rarely have I obtained Corallina by dredging in 

 greater depths, as, for example, on the north coast, at a depth of 

 about 14 metres, where it seems to be present in abundance. It 

 may be assumed with certainty, however, that this association has 

 a much wider distribution below the limit of low-tide than is 

 shown by the dredgings, and with exceptional low-tides it can be 

 seen that in many places the Co/'a//zna-vegetation covers the rocks 

 as far as the eye can reach. 



On a very exposed coast I have met with Corallina growing 

 socially in water-filled depressions at a considerable higher level, 

 sometimes on a level with the upper part of the Fnazs-belt. Here, 

 however, with the exception of the lowest part of the frond, it is 

 quite white in colour, and has evidently strayed outside its real 

 domain. The spores have been carried to this height above the true 

 Cora llina-beh by the beat of the waves, and have been retained in 

 the depressions. It can also thrive fairly well at this height during 



