Chapter XII 



MARINE ECOLOGY 



Ecology of Rocky Coasts 



The algal communities of the rocky coasts have attracted more 

 investigators, both botanical and zoological, than have those of any 

 other type of coast. This is because the fauna and flora are more 

 attractive, more extensive and more readily identifiable, and also 

 because the zonation is generally so well-marked. An observant 

 investigator of rocky sea coasts cannot help but be impressed by the 

 remarkably distinct zoning of the principal organisms : this is often 

 so pronounced that it is clearly evident from the decks of boats 

 passing by close to the shore. This zonation, moreover, is not con- 

 fined to any one region but is found almost universally throughout 

 the world. The vertical extent of the zones or belts depends on the 

 tidal rise, the greater the rise the more extensive each zone. Even in 

 the Caribbean where the tidal rise is about nine inches, it is possible 

 to observe a zonation, though each zone may not cover more than 

 two inches vertically. Any one of the major species commonly 

 occupies a very definite vertical range, but occasionally may be 

 found outside this range and then there is some cause, e.g. the 

 presence of a rock pool, which makes conditions favourable for its 

 existence. 



The numerous ecological studies that have now been carried out 

 in many parts of the world have involved a great number of investi- 

 gators. This has necessarily resulted in some lack of uniformity in 

 the results that have been obtained. In any one given area the actual 

 number of communities recognized depends primarily upon two 

 factors : 



(a) The locality: 



Some localities, especially those in colder waters, are very much 

 richer than others. In warmer waters the littoral marine fauna and 

 flora is much poorer though it may be quite rich in the sublittoral. 

 Within a region itself a rocky shore is usually richer than a boulder 

 shore, and a protected area is commonly richer than an exposed one. 



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