l6] VEGETATIONAL TYPES OF SEAS 527 



the Lichen Verriicaria maura which may form a continuous black 

 coating on the rocks. (2) Eiilittoral zone, often called simply ' the 

 littoral ', corresponding to the part of the shore undergoing more or 

 less regular emersion and submersion by tides or surf. This zone 

 varies in width from shores with no noticeable tides, where it includes 

 only the band regularly reached by surf, to those with wide tidal 

 amplitude, where various ecological conditions develop at different 

 levels and it is necessary to subdivide it into ' horizons ' or ' girdles ' 

 {see below). (3) Upper sublittoral zone, varying with the location 

 but characteristically extending approximately 20 metres downwards 

 from the low- water mark of ordinary spring tides to the lower limit of 

 abundant major benthic vegetation — i.e. to where the light-intensity 

 is markedly reduced and where there is little disturbance of the water 

 or rapid variation in the temperature. In temperate regions almost 

 all the Laminariaceae live in this zone ; indeed below it most of 

 the light-demanding species thin out and it is chiefly those char- 

 acteristic of deeper waters which persist. (4) Lower sublittoral zone, 

 extending from the lower limit of the upper sublittoral zone down 

 to the lower limit of at all plentiful benthic vegetation (usually 40-60 

 metres in total depth), and characterized by relatively constant 

 temperature and other conditions, and weak illumination. (5) 

 Infralittoral zone, extending from the lower limit of at all plentiful 

 benthic vegetation right down to the lower limit of photosynthesis. 



It may be noted that different belts or girdles of vegetation are 

 commonly discernible within the above main zones, being often 

 designated and named separately, and that it is sometimes useful to 

 recognize, above all the rest, an adlittoral zone of constant emersion 

 characterized by halophytes living a normal aerial life but able to 

 endure exceptional waves and sprays during storms. The salt is 

 concentrated by evaporation and may damage or deform ordinary 

 land vegetation. The adlittoral zone, and zones 3 and 4, are not 

 distinguished in the accompanying diagram (Fig. 170). 



Gymnosperms, Pteridophytes, and Bryophytes do not live in the 

 sea, and although some Angiosperms occur there, and a greater 

 number of Fungi and Schizophytes, the vast bulk of marine plant- 

 life is made up of Algae of extremely numerous and diverse types. 

 Much as the Raunkiaer system of life-forms that was outhned with 

 modifications in Chapter III may be useful to give some idea of the 

 physiognomic composition of a terrestrial flora when actual floristic 

 knowledge is lacking, so may a more recently proposed system of 

 biological typesof Algae be of service where marine flora is concerned. 



