Biocenosis of Mediterranean upper bathyal caves and ducts in total darkness

Description (English)

Very large submerged cavities especially present in drowned karstic networks, isolated little cavities and microcavities in heaps of stones and within certain concretions.
The caves in total darkness are enclaves of the aphotic area in the littoral area; they present extremely original environmental conditions, close to those found on the continental slope. The two key factors are the absence of light, which rules out photosynthetic organisms, and confinement, which rules out organisms which have a strong trophic requirement. Water renewal in the dark chambers is usually very slight or occasional and depends on local topographical, bathymetrical and geographical factors. The great hydrological stability is indicated by anomalies of temperature, extremely oligotrophic conditions, and biochemical parameters. Positive thermal anomalies are typical of caves with a rising profile (a frequent case in karstic caves) and negative anomalies have been noticed in the rare caves with a descending profile. The very great reduction in the trophic addition from the outside brings about a drastic selection of the animals established in this habitat. The rate of biological cover of the walls of this habitat may be 80 to 50% in the richest areas but can be almost nil in the most confined parts. The selection of trophic groups and morphological groups, as well as the spatial organisation, are governed by environmental conditions that are peculiar to each cave. This biocenosis includes a significant portion of typically deep-sea species, the most original of these being found in caves with a descending profile, with a thermal regime similar to that of the Mediterranean deeps.

Source: EUNIS habitat classification