288 



ALEEM 



developing leaves become readily colonized by the brown algae Ascocyclus 

 orbicularis, on top of w^hich grows Giraudya sphacelarioides. With the 

 advent of spring several microscopic forms attach themselves to the leaves, 

 amongst which members of the Melobesiaceae, Acrochaetium, Ectocarpus 

 and Polysiphonia become dominant. 



The following epiphytes have been identified on Posidonia leaves at 

 Abu Qir in late spring: 



GREEN ALGAE: 



Ulvella setchelli 

 Ulva riff id a 

 Endoderma viride 



BROWN ALGAE: 



Ascocyclus orbicularis 

 Hydroclatlirus dathratus 

 Colpomenia sinuosa 

 Ectocarpus mitchelli 



RED ALGAE: 



Acrochaetium 'virffatulum 

 Erythrotricliia carnea 

 Falkenbergia hillebrandii 

 Dasya sp. 

 Melobesia farinosa 

 Callithamnion corymbosum 

 Ceramium tenuissimum 

 Jania rubens 

 Amphiroa beawvoisii 



CladopJiora spp. 

 Enteromorpha linza 

 Phaeophila dendroides 



Giraudya sphacelarioides 

 Scytosiphon lomentaria 

 Casta ffnea mediterranea 

 Ectocarpus irregularis 



Acrochaetium secundatum 

 Erythrocladia subintegra 

 Laurencia obtusa 

 Lithophyllum pustulatum 

 Melobesia lejolisii 

 Polysiphonia spp. 

 Hypnea musciformis 

 A crosorium uncinatum 



Castagnea becomes a dominant epiphyte in the late spring and fronds 

 of this plant up to 20 cm in length are found in many places at Alex- 

 andria. Under such heavy loads of epiphytes, the leaves of Posidonia 

 drop ofE during the autumn and new leaves sprout in winter. 



Another interesting observation concerning these epiphytes was made 

 at Asafra rock in Alexandria where Posidonia grows in a wide area 

 from just below low water level down to a depth of several meters. The 

 Posidonia-Rtti thus formed slopes gently into the sea. The epiphytic 

 algae in this community vary both in quantity and quality during the 

 spring as one proceeds away from the shore. Close to the shore the 

 Melobesiaceae together with Ascocyclus and Giraudya are abundant. 

 At a distance of about 10 meters from the shore where the depth is 

 about one meter, Ectocarpus mitchelli and Enteromorpha linza are 

 dominant. Further away from shore and in deeper water, the dominant 

 algae is Castagnea. Probably this differential colonization of the distal 

 ends of the Posidonia leaves is connected with the light distribution at 

 such depths. 



