Biogenic habitats of Mediterranean mediolittoral rock

This habitat is formed by the biogenic, tridimensional, hard structures built by either the red algae Lithophyllum byssoides or the red algae Neogoniolithon brassica-florida associated with the gastropod Dendropoma cristatum (in the central Mediterranean) or D. petraeum. The rims of L. byssoides are generally found just above the mean sea level, in the mesolittoral zone, where waves break. They can reach more than one metre of vertical thickness. For this reason, the habitat is host to different assemblages from its upper portion, which is situated in the lower mediolittoral zone, to the lower, submerged one. The development of this type of habitat in specific areas of the Mediterranean depends on several climatic, hydrological and sedimentary conditions. It seems to develop better over calcareous rocks, on steep shores in areas with strong hydrodynamism and where the temperature of surface coastal waters is no lower than 14°C in the winter. Under these environmental conditions, the L. byssoides rims are more frequent in the northwestern Mediterranean, but they can also be found in Sicily and the Adriatic Sea. Mediterranean bioconcretions composed of N. brassica- florida and D. petraeum may grow for thousands of years forming huge structures of several metres wide.

These reefs are host to many species, which distribute differently over the bioconcretion depending on wave action and the position on the reef. In the seaward part of the reef, the reef crest, the concretion is made of shells of Dendropoma actively growing while Neogoniolithon cements the reef and triggers the vermetid settlement. Behind the reef crest, a shallow lagoon covered by photophilic algal communities develops. This part ends close to the shore, where Neogoniolithon and Dendropoma dominate again. Neogoniolithon-Dendropoma reefs better develop in southern Mediterranean areas although tiny reefs can be found across 40º N latitudes at their northern limit.

Indicators of quality:

The Lithophyllum byssoides rims are particularly vulnerable to physical impacts and trampling, and they seem to be very sensitive to environmental stresses related to water quality. Rims are very sensitive to the increase or decrease of the water level. The amount of dead L. byssoides thalli in the upper part of the reef can be used as a health indicator. Both reefs represent unique archives to reconstruct past Mediterranean climate and especially sea level oscillations.

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats