- ■= 



112 H. JONSSON 



Fucus vesiculosus grows highest and F. inflatus lowest. How the 

 species behave when left dry is mentioned in connection with each 

 association. 



The Fucus vesiculosus-association, as already mentioned, 

 is uppermost and often borders closely on that of Fucus spiralis. 

 It varies extremely in extent, according to the character of the coast. 

 The breadth may vary from about one foot on vertical rocks to 

 several fathoms on a gently sloping coast. 



Fucus vesiculosus extends right into the innermost part of the 

 fjords, which is generally considered a protected coast; if there is 

 a favourable substratum there, its growth may be fairly luxuriant. 

 It also grows very luxuriantly on slightly exposed coasts, i. e. where 

 a landward wind is sometimes both frequent and tempestuous, but 

 where breakers are extremely rare. If the exposure is increased, it 

 seems that F. vesiculosus not only decreases in number of individuals 

 but also seeks for shelter between the rocks. Then, gradually, it re- 

 treats lower into the littoral zone, and Ascophyllum, which is evidently 

 better able to withstand the heavy seas, advances. This is seen 

 very distinctly at Reykjavik, where the coast must be considered 

 somewhat exposed, because the south-west, west, and north winds 

 are frequently stormy and occasion heavy seas. If we take a bay 

 which is bounded by a rocky promontory, we see at the head of 

 it a luxuriant Fucus yeszcuZosus-association ; this extends out upon 

 the promontory, growing gradually narrower as it extends outwards; 

 in the vicinity of the point itself, the alga has commenced to seek 

 for shelter, and at the extreme end of the point it has disappeared 

 and Ascophyllum has occupied its place, and then Fucus vesiculosus 

 is either found not at all or only a few individuals of it occur 

 high up in the Ascophy Hum-belt. What is here seen on a small 

 scale is repeated on a larger scale on proceeding from the head of 

 the fjord outwards to the extreme point of the peninsulas. Thus, 

 Fucus vesiculosus was not observed on exposed points at 0ndver5- 

 arnes (the extreme point of Snsefellsnes) , while Ascophyllum and, 

 naturally, Fucus inflatus also, were found in abundance. On the 

 most exposed points of the Vestmannaeyjar Fucus vesiculosus was 

 also absent, while both of the others occurred plentifully. 1 Thus, 

 Fucus vesiculosus behaves in Iceland precisely as it does in the 

 Faeroes (Borgesen, 12, 11). 



1 Stromfelt (70) records Ascophyllum as growing above Fucus vesiculosus 

 at Holmanes in E. Iceland. 



