3i6 MARINE ECOLOGY 



of those plants that migrate down in winter, whilst response to 

 strong insolation determines the behaviour of those that move down 

 in summer. 



MOUNT DESERT ISLAND, MAINE 



For purposes of comparison the zonations that have been 

 described by Johnson and Skutch (1928) from this Western Atlantic 

 station are of considerable interest. It is a rough coast and the 

 vegetation is not only much poorer than that of most British 

 stations but also the zones are less distinct, whilst exposure to 

 storms is responsible for a splash zone of about 2 ft. The plant 

 aspect may vary from season to season and from year to year, but 

 this fact has already become emphasized in describing the British 

 vegetation. Johnson and Skutch recommended levels based on sea 

 level as the best means of recording the belts because it is more 

 convenient for purposes of comparison. This is undoubtedly true, 

 and those workers who adopt this more troublesome technique 

 nevertheless vastly increase the value of their investigations. The 

 littoral communities reported from this area, which has a mean tidal 

 range of 10*4 ft., are as follows: 



(i) A Porphyridiiim cnientum community, which is confined to 

 the spray zone, has four other species associated with the dominant 

 alga. 



(2) A Calothrix-Vernicaria community which ranges from 

 + 9-0 to — 12-0 ft. M.L.W. 



(3) A Codiolutn society that appears in summer only with its 

 lower limit (range +6-0 to —12-0 ft. m.l.w.) determined by the 

 submergence factor. 



(4) There is a Fucus vesiculosus — Ascophyllum community with 

 the former species predominant in the upper and the latter in the 

 lower portion of the zone. Range +5-0 to — i2-o ft. m.l.w. 



(5) A Bangia-Ulothrix-Urospora community confined to winter 

 and spring. Range +8-o to —12-0 ft. m.l.w. 



(6) An Enteromorpha community which is purely aestival. Range 

 + 3-0 to — lo-o ft. M.L.W. 



(7) A Porphyra community on the steep slopes from +2-0 to 

 -6-0 ft. M.L.W. 



(8) A Fucus fur catus community in the more shaded parts of the 

 area with a range of +2-0 to — 6-o ft. m.l.w. 



