Among the different habitats that characterize the Mediterranean marine environment there is also that of submerged caves.

 

Although the use of the singular is perhaps not appropriate, considering the differences among the marine caves that dot the coasts of the Italian peninsula and the islands. Starting from the origins and geological characteristics, for which each cavity, even compared to others in the same geographical area, ends up being unique with its own peculiarities. Some common and specific elements, however, allow us to identify three types of environments, linked to the mesolittoral caves, or the area that depends on the rhythm of the tides, to the caves where light penetrates even dimly and to the caves where darkness prevails.

Conditions that are decisive for the presence of some animal species typical of the rocky substrate instead of others. Animals, because it is the fauna that is prevalent everywhere, as it manages to adapt even to the most extreme conditions of the different microhabitats, while plants, which depend on light for photosynthesis, are not compatible with all caves. And in fact the bioconstructors inside the caves are represented only by animals, such as the sedentary polychaete Protula with the red tuft (Protula tubularia), which like other sedentary polychaetes builds the calcareous tube in which it lives. Precisely the welding between many tubes forms spectacular stalactites in the caves, which can even measure a few meters.

n the mesolittoral caves, which are completely or partially submerged depending on the movement of the tides, plants are present near the entrances or in points where light reaches. These are also encrusting red algae such as Phymatolithon lenormandii, which prefers shaded areas, Hildebrandia rubra with great adaptability and Catenella coespitosa, widespread in the Adriatic and on the western coasts of Italy. The fauna, on the other hand, is largely represented by sponges, coelenterates, bryozoans, serpulids and madrepores such as the yellow madrepore Leptopsammia pruvoti and the madrepore Polycyathus muellerae. Then there are crustaceans such as the crab Dromia personata, the mechanical shrimp or pink alifantozza (Stenopus spinosus), which lives up to 500 meters deep and, as for fish species, the black brotola (Grammonus ater), a nocturnal species that lives up to 700 meters. This type of cave in Sardinia was once frequented by the monk seal (Monachus monachus).

 

The semi-dark caves are populated by very brightly colored species such as the sea daisy (Parazoanthus axinellae), the red coral (Corallium rubrum), the yellow madrepore (Leptosammia pruvoti), the madrepore Phyllangia mouchezii, whose polyps are the largest in the Mediterranean, the madrepores that live in shaded areas Hoplangia durotrix and Caryophyllia inornata, as well as gorgonians. And there are hydroids, bryozoans, ascidians such as the orange Pyura dura, cicadas, lobsters, crayfish, shrimps and, among the fish, brown grouper (Epinephelus marginatus), brown meagre (Phycis phycis), conger (Conger conger) and the Marseille goby (Gammogobius steinitzi).

 

The presence and variety of animals in the dark caves is less, where species that usually live outside the caves at great depths, where little light filters, have adapted. Among these, the porifera Petrobiona massiliana, a living fossil that had been thought extinct, and then polychaetes, serpulids, foraminifera, crustaceans such as the cave crab (Herbstia condyliata), the red sea snail (Homalopoma sanguineum) and, among the fish, the orange cardinalfish (Apogon imberbis), which lives in burrows up to 250 meters, and the black brotola (Grammonus ater), also present at considerable depths.