Les cyanophycées endolithes marines: systématique, ultrastructure, écologie et biodestruction

The systematic study of the marine endolithic Cyanophytes in the region of Marseille, · including their ultrastructure, ecology and endolithic activity, permit the solution of a number of taxonomical problems and the description of ten different species of this algae. Extreme polymorphism was one of the features noted particularly with regard to the species Hyella ba/ani, in which the gradient of moisture and the nature of the substrate are the cause of morphometric variations. Three different species were noted among each Hyella and Hormathonema-Solentia complex. Variance analysis of the data revealed significant differences between certain mea_n parameters. In situ observations of the algae showed a direct endolithic character originating from the initial spore. Precisions conceming the cytology and chemistry of these endolithic Cyanophytes, together with indications of the importance of the structure of their sheaths for taxonomie purposes were provided by an ultrastructural study of the organisms. Certain characteristics reflect the adaptation of the algae to hard living conditions, and are directly related to their endolithic existence; these include: great thickness of the sheaths, considerable development of the thylakoios, and numerous storage substances. A loose network of polysaccharide microfibrilles, which fills the space. between the filament and the bored substrate, presumably serves during the exchanges between the algae and the substrate which lead to the desintegration of the surrounding limestone.