i6] 



VEGETATIONAL TYPES OF SEAS 



533 



Algae. In the lower sublittoral belt, down to some 30 or more metres, 

 gravelly or coarse sandy bottoms are characterized by an abundance 

 of branched and unattached Lithothamnium calcareum. Fig. 173 

 depicts a scene near the base of the girdles of Fuci on a rocky part 

 of the Atlantic coast of temperate North America, showing some 

 tufted Red Algae and large Kelps (Laminar iales) at the lower levels, 

 and Fig. 174 is a drawing of a typical Kelp. 



'••*#-■ 



Fig. 173. — Scene at low tide on a rocky sea-shore of the eastern United States. 



Above are seen luxuriant Wracks (Rockweeds, species of Fuciis), and below are 



a tufted Red Alga and some large Kelps (Laminariales). (Courtesy of Chicago 



Museum of Natural History.) 



On muddy tidal flats or shallow bottoms in sheltered situations. 

 Blue-green Algae often form a delicate investment which binds the 

 surface, while some forms of Fucus can live merely resting on mud 

 without being attached. Often they are partly embedded in the 

 surface and, with some other forms including various Green Algae 

 and halophytic terrestrial Angiosperms, favour estuaries where salinity 

 and other conditions vary markedly, such vegetation-types merging 

 into those of salt-marshes {see Chapter XII). The vegetation of 



