Clare Island Survey — Marine Algae. 15 21 



Prasiola stipitata Association. 



This association as it occurs in the Survey area is characteristic of bird- 

 cliffs ; but during the winter months it is found to a small extent outside these 

 areas. It is well developed on Caher Island, The Bills, and below the bird 

 colonies near the Signal Tower on Clare Island. The growth is most 

 abundant on the shady side of the cliffs, where it ascends to a considerable 

 height above high-water level, and forms the uppermost association of the 

 marine algae. With P. stipitata occurs, in the upper part, a certain amount 

 of P. crispa var. marina. The localities referred to are very exposed, 

 and, in rough weather, the cliffs are constantly soaked with spray, though 

 during calm periods the vegetation must remain dry for some days. The 

 fact that, in June, the small part of the south side of The Bills that was 

 examined showed no trace of Prasiola, suggests that in summer the growth 

 is confined to the more shady situations — a view which is supported by 

 points noted in the following paragraph. 



During the winter and spring months, Prasiola is found apart from birds. 

 Wide patches were noted at Eoonah and Old Head during the February visit, 

 and in April, 1911, in many spots on Clare Island. The growth is 

 practically pure, but is sometimes mixed with a certain amount of Calothrix 

 and Lyngbya ; it occurs on both smooth and rough rocks. In these localities, 

 as on the bird cliffs, Prasiola forms the uppermost algal vegetation, frequently 

 reaching the Lichina ccmfinis band, but more often forming patches between 

 that zone and Pelvetia. In several spots on the south shore of Clare Island 

 it was present only on rocks sloping landwards, where it was consequently 

 somewhat shaded ; but in others it was found on sun-dried rocks and well 

 above the uppermost Pelvetia. These rocks were fully exposed to the surf ; 

 and the plants, except during the calmest weather, would be splashed with 

 spray. By July all this vegetation had disappeared ; and it was not noted 

 during June of the previous year. 



The question of the connexion of Prasiola stipitata with bird-colonies is an 

 interestmg one. The preference shown by the fresh-water species, P. crispa, 

 for localities soaked with ammoniacal liquid is well known ; and its marine 

 relative evidently shares the same avidity for nitrogenous compounds. During 

 a trip to Belfast in connexion with the growth of Ulva in sewage-polluted 

 water, P. stipitata was, on the shores of Belfast Lough during April, noted 

 only around small drainage outfalls. In Lame Lough also a vigorous crop 

 was always to be found in similar situations. At Ballycastle, Co. Antrim, 

 however, as in Clare Island and Clew Bay, numerous patches of Prasiola 

 occurred (chiefly in shady spots) where there was no special supply of 

 nitrogenous food. 



