l6] VEGETATIONAL TYPES OF SEAS 53I 



Other seasons Red Algae predominate in poorly-lighted situations. 

 Some species even exist in different winter- and summer-forms. 

 Moreover, exposed habitats that support luxuriant vegetation during 

 winter may be almost barren in summer. 



In South Africa the girdles distinguishable in the eulittoral are, 

 uppermost, of Porphyra capensis which in places extends from the 

 upper limit to mid-tide level. Below this is often a ' bare zone ' 

 that may be largely devoid of macroscopic vegetation, succeeded by 

 a girdle formed of an association of two species of Chaetangium and, 

 farther down, by two or three other characteristic girdles. The 

 sublittoral is often dominated bv various Laminariales. 



3. The algal vegetation of cool-temperate seas is tolerably well- 

 known and often markedly diverse even in such closely adjacent 

 bodies of water as the North Sea and the Baltic, the former of which 

 is far more productive than the latter. The variation seems to be 

 in accordance with differences in the tides and salinity, which in 

 the North Sea are both very considerable, whereas in the Baltic 

 both are weak, so that its Algae are poor in species and development. 

 Yet in both instances, as in most cool-temperate seas. Brown Algae 

 predominate. They are chiefly represented by species of Fucus and 

 Laminaria or their allies, though manv smaller types also abound. 

 Red Algae are also represented by numerous types, but Green Algae 

 offer less variety, and the only at all widespread marine Angiosperms 

 are Eel-grasses. The eulittoral is much wider in the North Sea 

 than in the Baltic, and in some places bears more abundant vegetation 

 than does the sublittoral, though this is not the case in Scotland 

 (according to Mr. F. T. Walker in lift.). Actually, in the Baltic 

 Sea most of the marginal vegetation is commonly in the sublittoral, 

 as the tides are weak and ice frequently grinds against the upper 

 shores which are thereby rendered inhospitable for macroscopic 

 plants. 



In most exposed situations away from salt-marshes in cool- 

 temperate seas, macroscopic vegetation in the eulittoral is virtually 

 limited to rocky and bouldery substrata, any shingly, sandy, or 

 muddy beaches being largely barren. This is not, however, neces- 

 sarily the case low down, or, particularly, in some estuaries and 

 sheltered creeks, where plentiful between-tides vegetation may de- 

 velop even on ' soft ' bottoms. Unlike the situation in warm- 

 temperate regions, in cool-temperate seas the algal vegetation of winter 

 tends to be poorer than that of summer, which for most species is 



