Cyanophycées marines endolithes colonisant les surfaces rocheuses dénudées (Etages Supralittoral et Médiolittoral de la région de Marseille)

The object of this study was the endolithic blue-green algae of the upper and middle litoral zone of the rocky coast near Marseille.

Difficulties in determining these algae cropped up very soon because of their strong plasticity. To ascertain whether there were different species of algae or only different ecological types of the same species, two series of experiments were carried out in the region around Marseille: 1. small rock splinters from various places were cemented into place in the above-mentioned zones. 2. The regrowth of rock surfaces that were cleared of algae was observed. Moreover cultures of the individual species were made to find an unequivocal solution to the systematic and ecological problems of these algae.

Only the results of the tests on recolonization of the rock surface by algae are dealt with in this paper. According to our observations, the Entophysalis deusta (Men.) Drouet and Daily developed in different patterns depending on the degree of moisture. In the upper litoral zone where the amount of moisture is less significant it takes on epilithic forms that do not penetrate into the rock. In the more humid middle zone they prevail in an endolithic stringy form. It is interesting to note that the various forms always appear in the same order; thus with increasing moisture one finds: Gloeocapsa, Entophysalis, Scopulonema (forms of the upper litoral zone) and Hyella caespitosa, Hyella tenuior (forms of the middle zone). Other species such as theHormathonema that grow in the same biotope as theEntophysalis seem to react differently to outside stimuli.

The conjectures concerning the plasticity of the Entophysalis deusta confirm Drouet and Daily’s theory. Yet this hypothesis needs to be confirmed through cultures of the forms observed.