282 ALEEM 



2. Scytosiphon lo?nentaria. This species occupies the zone just below 

 the blue greens, in an uninterrupted belt, and, like Nemalion, disappears 

 completely in summer. Its place is taken by Enteromorpha compressa, 

 young growths of Padina, and Polysiphonia phleborhiza, particularly 

 when the substratum is covered with sand and shell fragments. 



3. Laurencia papulosa. This extends from the mean water level 

 down to some 20 cm below the surface and remains throughout the year, 

 shedding its branches in later summer. Heavy masses of Jania rubens 

 cover it during the summer. 



The Upper Sublittoral Region : 



4. Cystoseira-Sargassum. This characteristic belt occupies the space 

 on the ridge from below the Laurencia down to 80 cm. It is better de- 

 veloped and wider on ledges subject to wave action, especially at the 

 distal end of the ridge facing the open sea and on the borders of the 

 channel intersecting the ridge. Cystoseira crinita (?) and Sargassum 

 limfoliiim are the two chief species in this community, which also har- 

 bors a number of epiphytes such as Ectocarpus, Ceramium, and Poly- 

 siphonia spp. Jania rubens forms a carpet over the substratum and occurs 

 also as an epiphyte on other algae. 



5. Halopteris filicina — Padina pavonia. These two species grow in 

 a well developed community attaining a considerable size, especially on 

 the flat sandy bottom between the ridge and the Posidonia-Cymodocea 

 boundary toward the shore, in relatively calm water (fig. 2). As Halop- 

 teris can tolerate more agitated water, it extends along the ridge all 

 the way below the Cystoseira-Sargassum community, at a depth exceed- 

 ing 1 meter. Older growths of Halopteris and Padina form good sub- 

 strates for a large number of epiphytic algae. 



6. Caulerpa prolifcra. This species occupies a unique position. Not 

 only does it almost always form the boundary between Posidonia and 

 Cymodocea (fig. 1) but it also grows in patches among the Cymodocea 

 and between the Cymodocea and the shore. Dasycladus clavaeformis also 

 grows in the latter habitat, but only in small patches on stones covered 

 with muddy sand. 



Of particular interest are several submerged grottos occurring at 

 different levels along this coast. The occurrence of such grottos below 

 the present sea level (fig. 4) is a good indication of the subsidence which 

 took place along the coast of Alexandria in historical times. This is 

 indicated by the presence of a belt of islets running parallel to the coast, 

 at a short distance from the latter; these were once a part of the shore 



