p. 133- 139 CONTRIBUTIONS TO THE STUDY OF THE ELEMENTARY CHEMICAL COMPOSITION OF THE PRINCIPAL MACROPHYTES ALONG THE ROMANIAN COAST OF THE BLACK SEA Natalia Rosoiu and A.S. Bologa Romanian Marine Research Institute Constanta Abstract The seasonal variations of Na+, K+, Ca2+ and Mg2+ contents of Enteromorpha linza, Cladophora sericea, Cl. vagabunda, Cystoseira barbata, Ceramium elegans and Zostera marina + Z. nana are presented; the concentration of these elements varies according to their taxonomic pertaining, provenience location and season.