Study of the population structure of the corallinale algae Lithophyllum stictaeforme/cabiochiae, coralligenous bioconstructor

Mediterranean’s coralligenous concretions (Habitat 1107 – Habitat directive 92/43 EEC) develop on the low sublittoral and high circalittoral zones and are important marine ecosystems in terms of structural complexity and marine biodiversity. Calcareous red algae of the order Corallinales constitute the basal builders of the coralligenous frameworks. The taxonomy of this group of species is complicated. The endemic Mediterranean rhodophyte Lithophyllum cabiochiae is one of the major contributors to the primary production and the fixation of calcium carbonate under sciaphilic conditions. It is a perennial species of algae with slow growth rates and unknown dispersal capacity. In the current study, molecular markers were used in order to precise the specific limits of Lithophyllum spp and describe the distribution of genetic diversity along geographically and ecologically varying locations in the area of Marseilles (North-West Mediterranean). The sampling protocol was developed in the framework of CIGESMED SeasEra Project. A minimum of 30 individuals were collected along inter-calibrated distances, at 30 m depth at each locality. The main geomorphological features were also recorded insitu. The analysis of the nucleotide sequences from two markers revealed 4 different clades, strongly suggesting that there are different species. Electronic microscopy observations confirm that morphological characters used for Lithophyllum taxonomy need revision. Genetic diversity within the bay of Marseilles appeared spatially structured , implying geographical barriers to the species dispersal and/or local adaptation. This kind of information provides data on the connectivity among different coralligenous sites and could be useful for decision-making processes concerning management and conservation issues