THE MAIITNE ALG-li; OF GUERNSEY 41 



Zour of Calcareons Alf/ce. 

 This Zone can be definitely traced round the island excepting 

 where patches of sand or Zostera beds intervene. It is the widest ot 

 all the zones, spreading over the whole of the Littoral and Sub-littoral 

 re<>-ions and extending beyond all other algcX3 to a considerable depth. 

 Its maximum development is round Pleinmont m extreme exposure. 



Comllina officinalis is at first short and tufted, mcreasmg gradu- 

 ally in length as low-water mark is approached : it is replaced at low- 

 tide level by G. squamata. O. corniculata and G. mediterranea 

 appear with greater protection from storms. ^ £ xi. 



Lithothamnion Lenormandi is always the uppermost ot the 

 calcareous encrusting species, appearing a little above the Mid-httoral. 

 It prefers shady positions in chinks and crannies where some moisture 

 is retained, and descends below half tide, mingling with and giving 

 r)\^Qii io L. incrusf cms. 



The delicate and beautiful LithopliijUum lichenoides forms a 

 constant feature on the upper edges of rock-pools from half down to 

 low-tide levels along the west, east, and north coasts. L. incrustans 

 lines basins and pools up to the water's edge, then ceases abruptly, 

 beino- unable to withstand desiccation. It occupies the lower Mid- 

 littoral from about half tide to nearly low-water mark, and then 

 mingles with LitJiotli amnion polymoijyhum. Where rocks have a 

 smooth surface these Lithothamnion s, by lining the pools and basins, 

 create a rouo-hness which afEords a foothold for other alga?. L. iwly- 

 morphum belongs exclusively to the Sub-littoral regions and beyond. 

 It has a rounded knobby thallus. 



SUB-LITTOEAL REGION. 



The various species of brown algse connecting the Sub-litioral 

 with the Littoral region, form a more or less continuous band along 

 the shore, consisting cliiefly of Bifurcaria tuherculata and Gysto- 

 seira spp. Where conditions of moderate shelter prevail, Iliman thalia 

 lorea mingles with the Bifurcaria or forms patches over the rocks 

 and boulders at the same 'level; but with extreme exposure it dis- 

 appears from the open and occurs only in locally sheltered ]>ools. The 

 condition of things therefore differs from that described by Cotton 

 « for Clare Island where he alludes to the plant as charactenstic of 

 moderately exposed shores. On the other hand, his statement that 

 this alga is of a surf -loving habit in the British Isles is fully corrobo- 

 rated in Guernsey. 



Zone of Galcareous Alga. 



The Zone of Calcareous Algfe is continued from the Littoral and 

 extends far down into the Sub-littoral region, mostly as an under- 

 growth of other species. Gorallina squamata and Lithothamnion 

 polymorphum are most in evidence; they flourish best in fully ex- 

 posed situations. With more moderate conditions, the followmg^ 

 plants are often found creeping over the surface of L. polymorphum'. 

 Qelidium crinale, Nitophyllum ramosim f. repens, Zonaria parvula. 



