Association with Lithophyllum byssoides

Description (English)

The association with the Lithophyllum byssoides is the highest biological construction in the Mediterranean. When the water is calm, the rim emerges completely, and its outer edge extends to 20 to 30 centimeters above the water, a position that is possible because it is present where there is strong wave action and because of the porosity of the formation. The height above the middle level is linked to the local degree of roughness. In crevices and little coves that are open to the swell and sheltered from the direct rays of the sun, it may be of considerable width and thickness. Rims that are over two meters wide have been seen. The rim is formed by the stacking up of calcareous Lithophyllum byssoides thalli with a re-crystallising of the deeper layers. Three successive layers may be seen, whose respective thickness depends on environmental and local history conditions. Only the upper part is alive. At the base of the living part of the Lithophyllum byssoides many endolithic Cyanophyceae (Brachytrichia, Calothrix and Entophysalis genuses) can be observed. The lower surface of the ledge, often below the average level, is dead and covered with sciaphilous animal and plant assemblages. Destructive animals (Cliona, Lithophaga) bore into the rock, creating cavities which contain an upper infralittoral type of fauna and flora. In less favourable environmental conditions, the Lithophyllum constructions are mere pads in the mediolittoral area.

Source: EUNIS habitat classification