Distribution and genetic variation of two bioconstructor coralline algae (Lithophyllum byssoides (Lamarck) Foslie and L. stictaeforme (Areschoug) Hauck) along the Italian coasts

Coralline red algae represent a worldwide component of hard-bottom coastal communities, where they play a key role in many ecological processes. Some species are ecosystem engineers that produce biogenic platforms, reefs and other calcified structures providing a wealth of habitats for many other species, especially in temperate seas. In the Mediterranean Sea these bioconstructions are widespread and occur both in the littoral zone (trottoirs of Lithophyllum byssoides) and in the sublittoral zone (coralligenous bottoms, where coralline algae are one of the main constituents). A detailed knowledge of their distribution and composition is essential for their conservation, but molecular data assessing taxonomic identity and population structure in corallines are extremely limited. The distribution and genetic variation in two important bioconstructor corallines, Lithophyllum byssoides and L. stictaeforme (Corallinales, Corallinaceae) are investigated using sequences of the plastid psbA gene and mitochondrial cox2,3 spacer. Populations of L. byssoides occur on all parts of the Italian coastline where rocky shores exist and the molecular data show that Mediterranean populations of this species represent a sister lineage to Atlantic populations. L. stictaeforme is widespread along the Italian shores, particularly along the Ligurian and Tyrrhenian sides. In molecular phylogenies Mediterranean populations of L. stictaeforme form a well-supported clade, to which North Atlantic Lithophyllum spp. are the closest relatives. Overall the results indicate a high genetic variability in these species, with the possible existence of cryptic species.