Biocoenosis of Mediterranean semi-dark caves and overhangs

Description (English)

The front parts of caves and tunnels, overhangs and vertical faces. This habitat constitutes the transition between the beds of hard substrata with concretions, where the calcareous algae and other sciaphilous algae play a basic part, and the caves in total darkness, where the physical environment is extremely selective and the population is exclusively animal. In this habitat, light and water movement diminish rapidly the greater the distance from the entrance to the cave (i.e. the open sea) and according to topographical factors. As a result, there is a tendency to environmental stability, which increases with the distance from the entrance, and a drop in the presence and abundance of certain groups of organisms (like passive filterers). This biocenosis is characterised by a frequent juxtaposition of facies, partly linked to the variability of the habitat caused by the environmental topography, but also certainly resulting from historical recruitment events. The biocenosis of semi-dark caves only contains a few rare sciaphilous algae, restricted to the area that is nearest to the outside environment, and has no herbivores. The trophic network is thus composed of filterers, scavengers and carnivores only. A confinement appears following a gradient that goes from the outside to the inside of the cave, with a drop in external additions, and a development of organisms that are not very demanding or are well adapted to exploiting a weak, unpredictable trophic resource.

Source: EUNIS habitat classification