Structure of a deep-water community of Halimeda tuna (Chlorophyceae, Caulerpales) from the North-Western Mediterranean

Abstract

A deep-water community dominated by Halimeda tuna and Mesophyllum lichenoides is described from the rocky bottoms of the North-Western Mediterranean. Other sciaphilic algae such as Udotea petiolata, some Peyssonnelia species and Lithophyllum expansum are also abundant. Algal biomass ranges between 1200 and 2100 g dw m^-2 while percentage coverage ranges from 180 to 400%. The variations observed in algal coverage adequately describe the seasonal pattern of the community, which is characterized by a high development of erect algae in summer months and a low development in winter. The species richness, as well as both species and pattern diversity reach a maximum in summer. Summer's maximum irradiances and the low irradiances received between November and February seem to account for the seasonal pattern described above. Community structure and environmental factors affecting the deep-water Halimeda populations from the North Western Mediterranean are compared with those found in other deep-water seaweed communities from the Mediterranean and other seas. Finally, the phytosociological affinities between these Halimeda populations and the deep-water Mediterranean associations previously described is assessed.