THE BALTIC SEA 

 Table 124 



301 



plants decrease in size the farther they penetrate into the diluted waters of the 

 Baltic, and this is accompanied, as in the case of the zooplankton, by sterility. 

 Thus, for example, the small forms Polysiphonia nigrescens and Rhodomela 

 subfusca, inhabiting the inner parts of the Baltic, multiply very rarely 

 (S. Sagerstrale, 1957). 



Propagation to the east. Just as with the fauna the Darss ridge sets a definite 

 limit to the propagation of marine algae to the east. To the west of the ridge 

 there is an abundance of such forms as Chaetopteris plumosa, Stvlophora 

 tuberculosa, Spermatochnus paradoxus, Laminariajiexicaulis, Fueus eeranoides, 

 Ascophyllus nodosum among the Phaeophycae and different species of Por- 

 phyra, Chondrus crispus, Cvstoclonium purpurescens, Rhodimenia palmata, 

 Delesseria sanguinea, Polysiphonia urceolata and other red algae. None 

 of this luxuriant marine flora extends eastward of the Darss ridge, and 

 the flora of the Baltic Sea east of the ridge contains such brown algae as 

 Fucus vesiculosus, Chorda /ilium, Ch. tomentosum, Elachista fueicola, Dictyo- 

 siphon foeniculaceus, Gobia baltica, Strichtyosiphon (Phlocospora) tortilis, 

 Sphacelaria racemosa, Ectocarpus siliculosus, E. confervoides, Pylaiella 

 litoralis. Limnaria saccharina reaches the shores of Bornholm, and Fucus 

 serratus — Gotland ; among the red algae are Asterocystis ramosa, Phyllophora 

 brodiaei, Polysiphonia violacea, P. nigrescens, Rhodomela subfusca, Ceramium 

 diaphanum, Furcellaria fastigiata and others. As for the green algae, various 

 species of Ulva, Monostroma, Enteromorpha and Chaetomorpha may be 

 added. 



This composition of the flora is typical for the areas with a surface summer 

 salinity of about 8% . A sharp decrease of marine forms is encountered again 

 at the entrance to the Gulf of Bothnia and at the transition from its outer to 

 its inner part. 



Floral plants occupy a significant place in the coastal vegetation of the 

 Baltic Sea; their distribution according to salinity is given in Fig. 144a. 



The algae of the Baltic Sea extend to a depth of 25 m ; the number of species 

 according to Hessner is given in Table 125. The red and brown algae descend 

 deeper than the others. 



Only the most hardy forms reach the northern parts of the Gulf of Both- 

 nia (Fig. 144), namely: Fucus vesiculosus, Chorda filum, Elachista fueicola, 



