posidonia and cymodocea 293 



Moderately exposed modes : 



11. Competition between Posidonia and Cymodocea is great in such 

 modes and the former ultimately eliminates the latter. This occurs 

 in shallow water near the shore and also at the back of projecting 

 rocks facing a water current. 



The lagoon : 



12. Posidonia grows in the outer northern side of the lagoon at Abu 

 Qir, subject to the currents, while Cymodocea occupies the inshore 

 calm part, together with tropical algae which reach maximum pros- 

 perity there. 



Structure of the Posidonla and Cymodocea Communities : 



13. A dense and diverse flora of algae finds shelter as epiphytes on the 

 leaves and rhizomes of Posidonia. Light is an important factor 

 affecting the distribution of these algae. Epiphytes on the leaves 

 differ also in quantity and quality according to season and depth 

 below the surface. Some of these epiphytes follow a certain suc- 

 cession in colonizing the leaves of this grass. 



14. Epiphytes on rhizomes of Cymodocea are scarce; those on leaves 

 are more abundant in shallow than in deep water. 



LITERATURE CITED 



Aleem, a. a. 



1951. Algues marines de profondeur des environs d'Alexandrie (Egypte). 

 Bull. Soc. Bot. France. 98:249-252. 



Feldmanv, J. 



1951. Ecology of marine algae. In Smith, Gilbert, ed. Manual of Phycology. 

 Chronica Botanica. 27:1-375. 



MOLIXIER, R. ET J. PiCARD 



1952. Recherches sur les Herbiers de Phanerogames marines du littoral 

 mediterranneen fran^ais. Ann. Inst. Ocean. Paris. 27:157-234. 



1953. Notes bio'ogiques a propos d'un voyage d'etude sur les Cotes de Sicile. 

 /^fi. 28:163-188. 



