328 THE ALGAE 



(b) The personal factor: 



Each investigator will tend to have a somewhat different concept 

 of what comprises an algal community. The number of communi- 

 ties recognized will also depend upon the time and thoroughness 

 with which the shore is examined. 



The terminology that has been employed for naming the com- 

 munities has led to no littie confusion. Algal ecology commenced 

 after terrestrial ecology and so some investigators have attempted 

 to apply terms used in the latter to the former, whereas others have 

 considered that the conditions are sufficientiy different to make 

 this appUcation impossible. Cotton (1912), for example, recognized 

 five algal formations at Clare Island in western Ireland : 



(i) Rocky shore formation. 



(2) Sand and sandy mud formation. 



(3) Salt marsh formation. 



(4) River mouth formation. 



(5) Brackish bay formation. 



These were subdivided into associations, the rocky shore forma- 

 tion containing the associations of the exposed coast and of the 

 sheltered coast. Although the term 'association' was applied to these 

 communities, it is probable that many of them were really 

 'societies' in strict ecological nomenclature. At Lough Ine in south- 

 west Ireland Rees (1935) classified the formations on a different 

 basis and he recognized only two, the exposed and sheltered coast 

 formations. Rees further used the term 'association' for those com- 

 munities where species that are associated with the dominants are 

 controlled by the same factors. The difficulty of this criterion is the 

 time involved in proving experimentally that certain factors do 

 control the distribution of the species concerned. Seasonal com- 

 munities, or those with local dominants, were termed societies, 

 whilst the term 'zone' was used for those algal belts which possess 

 horizontal continuity with well-marked upper and lower limits. 

 However, the term zone has essentially a geographical connotation, 

 e.g. temperate zone, tropical zone, so that it is best employed in a 

 biogeographical sense, and the word 'belt' used for the marked 

 horizontal communities. 



In New Zealand Cranwell and Moore (1938) termed the group 

 of successive belts that follow one another vertically an 'associa- 

 tion complex'. The horizontal belts are normally continuous, but 

 they can be interrupted occasionally by another community, e.g. 



