ECOLOGY OF SALT MARSHES 



327 



marshes light and space relations, rather than factors relating to 

 level, influence the distribution of the various species. Whilst this is 

 undoubtedly true there is no doubt that the increasing height of a 

 marsh with its consequent greater exposure does nevertheless 

 effectively determine the upper height to which many plants can go. 

 The species to be found on the higher marshes in Norfolk are 

 either fucoids or gelatinous Cyanophyceae, both of which have the 

 power of retaining moisture. The more delicate Chlorophyceae are 

 more or less confined to the lower levels. On the other hand a 



11 ui IV V VI VII vm IX X 



Fig. 194. Distribution in time of the algal communities on the salt marshes at 

 Canvey and Dovey. I. General Chlorophyceae. II. Marginal diatoms (two com- 

 ponents, (A) those with a winter maximum ; (B) those with a summer maximum). 

 III. Marginal Cyanophyceae. IV. Ulothrix community. V. Enteromorpha 

 minima. VI, Anabaena torulosa. VII. Filamentous diatoms. VIII. Autumn 

 Cyanophyceae. IX. Phormidium autumnale. X. Rivularia-Phaeococcus . XI. Pel- 

 vetia canaliculata. XII. Catenella-Bostrychia. (After Carter.) 



dense phanerogamic vegetation, such as one finds on the south 

 coast marshes where the tall Spartina Townsendii must lower the 

 light intensity considerably, does reduce the quantity of algal 

 vegetation. A similar state of affairs has been observed on the 

 grass-covered marshes of New England. 



From data available it is possible to compare the distribution in 

 space (e.g. among the different phanerogamic communities) and 

 time of the marsh communities recorded from Canvey, Dovey and 

 Norfolk. Figs. 194 and 195 show the distribution of the Canvey and 

 Dovey communities and they should be compared with figs. 196 



