POSIDONIA AND CYMODOCEA 



287 



BROWN ALGAE: 



Padina pavonia 

 Dictyopteris membranacea 

 Hydrodathrus clathratus 

 Cladostephus <verticillatus 

 Ectocarpus spp. 



GREEN ALGAE: 



Cladophora prolifera 

 Dasycladus clavaeformis 

 Valonia utricularis 

 Bryopsis spp. 

 Ulva rigida 

 Codium dichotomum 

 Halimeda tuna 



RED ALGAE: 



Peyssonnelia rubra 

 Pseudolithophyllum expansum 

 Mesophyllum lichenoides 

 Griffithsia opuntioides 

 Pterocladia capillacea 

 Halopithys pinastroides 

 Botryocladia botryoides 

 Laurencia pinnatifida 

 Falkenbergia hillebrandii 

 Grateloupia filicina 

 Callithamnion granulatum 



Halopteris filicina 

 Colpomenia sinuosa 

 Nereia filiformis 

 Sphacelaria pennata 

 Cystoseira fimbriata 



Cladophora pellucida 

 Udotea petiolata 

 Halicystis parvula 

 Ulva lactuca 

 Chaetomorpha sp. 

 Caulerpa prolifera 



Peyssonnelia squamaria 

 Melobesia farinosa 

 Neomonospora furcellata 

 Gelidium spp. 

 Champia parvula 

 Rytiphloea tinctoria 

 Laurencia obtusa 

 Heterosiphonia <ui'urdemanni 

 Rhodymenia ardissoni 

 Gigartina acicularis 

 Jania rubens 



Padina and Halopteris are especially abundant where the leaves of 

 Posidonia are not so dense. They can even grow on stones washed on 

 to the Posidonia-Reei and in places where parts of the reef are eroded. 

 Dictyopteris, on the other hand, requires more shade and is more abun- 

 dant in deeper prairies, or where dense leaves are found. At Abu Qir 

 the Dictyopteris from the center of the Posidonia-Reei attains a con- 

 siderable length, some fronds measuring over 60 cm in length. 



The algal flora associated with Posidonia in deep water is less 

 abundant and is mainly dominated by calcareous algae such as Pseudo- 

 lithophyllum and Lithothamnion. 



Some of the algae mentioned carry secondary epiphytes, mostly 

 microscopic red and blue-green algae, which are not listed here. 



The fauna associated with the rhizomes of Posidonia is no less im- 

 portant than the algae. Cirriped worms secrete their calcareous tubes 

 there, while a diverse fauna of holothurians, chitins, and polychaetes find 

 shelter on the sand deposited over the rhizomes. The Posidonia biotype 

 also shelters echinoderms in abundance, as well as several sponges and 

 hydroids. 



The upper third of the Posidonia leaf is usually the part colonized 

 by epiphytes, which show a periodic development according to season, 

 being most abundant during the spring. In the early winter the young 



