Maerl facies distribution offshore Cilento Peninsula (Tyrrhenian Sea, Italy).

Quantifying the areal distribution of maërl and coralline carbonate production and accumulation is instrumental to define their role on present shelves sedimentation and in the carbonate budget of the Mediterranean Sea. The Cilento coastal area (eastern Tyrrhenian Sea) has been mapped and characterized by acoustic survey techniques combined with sediment sample analysis. Maërl-beds are reported for the first time off the Cilento coasts, where calcareous red algae are the most important carbonate producer between 40 and 60 meter of water depth (w.d.). Within the study area maërl-beds dominate on submerged terraces located at variable w.d. between 42 and 52 m. The preferred distribution of maërl-beds on submerged terraces is associated to the role that terraces exert in the local circulation dynamic, deviating bottom currents and thus preventing the detrimental sediment accumulation on maërl. We calculated the coralline carbonate accumulation from the percentage cover of coralline algae (by thin section mapping) x 1-cm thick layer of sediment x measured coralline density. The total coralline cover (live plus dead) in the Cilento area is 13.96 km2, with a total 316800 t of algal carbonate in the surface 1cm-thick layer, that is to say 20430 g m-2. Living maërl is recorded at a depth of 47 m, with a live coralline cover of about 40% over a minimum area of about 1.19 km2. This live maërl has a thickness of about 1 cm and is mostly composed of unattached branches of Lithothamnion corallioides Crouan & Crouan, 1867. The molluskan association of the maërl bed is dominated by characteristic species of the Coastal Detritic Biocoenosis. Living coralline production rate has been calculated as weight of live corallines in 1-cm thick layer x 100 y-1 x total area-1 and corresponds to 90.8 g m-2 y-1