Different rhodolith assemblages host distinct associated species but similar ecological groups: A case study in NW Mediterranean Sea

Rhodolith beds represent the most widespread and studied facies of the coastal detrital bottoms characterized by macroids of living encrusting organisms. In the Mediterranean Sea, four rhodolith facies have been described: i) boxwork rhodoliths; ii) maërl; iii) pralines; and iv) unattached Peyssonneliales. Although lists of species associated with Mediterranean rhodolith beds have been published, no comparison among the species associated with different rhodolith facies are available. This paper compares the species associated with the four above-mentioned rhodolith facies sampled in the Tuscan Archipelago (Italy). These facies shared most of the 12 rhodolith species identified (10 Corallinales and 2 calcified Peyssonneliales), but with different abundances. Only three associated species (out of 377) were common to all four rhodolith assemblages, which however were all characterized by the abundance of the ecological group of the species characteristic of the biocoenosis of the Coastal Detrital bottoms. Therefore, rhodolith facies were better described in terms of ecological groups rather than species composition. Similar studies in other sectors of the Mediterranean Sea are needed to generalize this result, and the comparative study of other macroid facies, namely coralliths and bryoliths, would also be of interest.