Clare Island Survey — Marine Algae. 15 55 



(c) Ascophyllum and F. vcsiculosus. — The irregularities in the vertical 

 range of Ascophyllum and F. vesicidosus have been noted by several writers. 

 Borgesen calls attention to the difference in the observations of Stromf elt in 

 Iceland, and Eosenvinge in Norway ; and records irregularities noted by 

 himself in a single locality in the Faeroes. He comes to the conclusion that 

 the difficulty may be explained by the factor of exposure and small differences 

 in local topography. No doubt this solution is correct with regard to many 

 localities; but in Achill Sound it was found inadequate, and a further 

 explanation had to be sought for. It has always been assumed that in 

 England the Ascophyllum zone begins slightly above that of F. vesicidosus, 

 and Miss Baker ('09) gives figures which support that view. This sequence 

 is found on the stone embankments of Achill Bridge and in other places ; but 

 on the shores in Clew Bay, as often as not, the reverse order obtains. The 

 explanation, so far as the sheltered waters of the Survey area are concerned, 

 was found to be largely one of anchorage. Ascophyllum requires a stronger 

 mooring than Fucus ; and on the sandy shores of Clew Bay where the stones 

 in the upper part of the beach are small they are insufficient for Ascophyllum, 

 though well able to provide a mooring for a short growth of Fucus. The 

 absence therefore of the Ascophyllum-zone, or the presence of scattered plants 

 only, is explained by the absence of rock and large stones at the right level, 

 or the presence of isolated rocks only. In many parts of the Sound the 

 anchorage is sufficiently good to allow Ascophyllum to flourish at all levels, 

 and then the normal sequence is almost invariably maintained. Very small 

 stones suffice for both F. spiralis and F. vesicidosus ; but it is unusual to find 

 even young plants of Ascophyllum on stones. The last-named shows a decided 

 preference for boulders, from which it hangs in festoons. The stone-attached 

 Fucus- vegetation is essentially one of very sheltered water, and could not 

 exist were there much wave-action. Where the stones are light the growth 

 is small, and if, by reason of a long spell of quiet weather, an extra amount 

 of foliage should be produced, a number of plants will be displaced with the 

 first ruffling of the water. 



Ascophyllum fruits in late winter and spring. In summer and autumn a 

 large amount of vegetative growth takes place ; and young receptacles are laid 

 down in autumn. The latter begin to ripen in March, the main crop of spores 

 being liberated in April and May. The effect of exposure has been dealt 

 with above. 



The Fucus vesicidosus belt is the widest. On flat shores it ranges from 

 20 to 80 yards, in the upper part usually accompanied by Ascophyllum, but 

 near low water often pure. No attempt was made to determine all the forms ; 

 but the most abundant is the ordinary type. Var. vadorum is also common. 



