Marine caves are peculiar coastal environments characterized by sharp physical, chemical and hydrodynamic gradients. For example, light attenuation is responsible for the lack of photosynthetic production in the inner parts of caves. Thus, the distribution of marine organisms is related to these selective environmental features, which allow such caves to be subdivided into distinct ecological zones. On a small scale, marine caves show high biodiversity and habitat diversification (both rocky and sandy). For this reason, they can be considered "miniature natural zoos" where a large variety of marine life, including deep sea species, is represented. From this point of view, the study of marine caves may promote a better understanding of the complex relationships between distribution patterns of organisms and ecological factors. Moreover, marine caves are particularly relevant in regard to ongoing marine protection programs of the Italian Government.

Salento is a karstic peninsula located in southeastern Italy that contains one of the most significant concentrations of marine caves along the Italian coast (Fig.1) (Onorato et al., 1999). At present, 53 submerged caves have been described. However, the geomorphologic uniformity of the coast suggests that many more await discovery. The well-studied Zinzulusa cave is particularly noteworthy from a biological perspective. The interior of this cave contains an anchialine pool, "Il Cocito", inhabited by a stygobiotic fauna including the recently described endemic sponge Higginsia ciccaresei (Pansini & Pesce, 1998) (Photo 1).

The high density of marine caves along the coasts of Salento provides considerable opportunity for biological investigations. Studies on the ecology of marine caves have been undertaken to identify environmental issues and to safeguard these marine ecosystems. Although they have suffered minimal environmental degradation, in fact, they require careful management because of their fragility. The Salento, moreover, is affected by a heavy anthropogenic pressure as a consequence of the date-mussel fishery which leads to desertification of shallow rocky bottoms (Fanelli et al., 1994). Thus, marine caves are important sites for preserving the environmental integrity of those areas.
A preliminary survey was carried out in the underwater cave "Grotta delle Corvine" (Belmonte et al., 1999; Denitto et al., 1999) (Fig. 2; Photo 2). The results displayed a high biodiversity of sessile fauna (only among sponges, 46 species were recorded) and some uncommon patterns of colonization of hard substrates (Photo 3; 4; 5a; 5b; 6a; 6b). Also noteworthy is the presence on the soft bottom of a dense population of the ceriantid Arachnanthus oligopodus (Photo 7), formerly reported only from a submerged cave near Marseilles, France (Harmelin et al., 1987). The plankton, still under study, contains many components of the so-called hyperbenthos (mainly copepods).

Figure 2: Profile and plan views of "Grotta delle Corvine".		Photo 2: "Grotta delle Corvine" site. Photos 2-7 were taken in Grotta delle Corvine by F. Denitto.		Photo 3: Red algae such as Peyssonellia squamaria and Lithophyllum frondosum are very abundant within 5 m from the cave mouth.

Photo 4: A rich population of the yellow anthozoan Leptosammia pruvoti characterizes the rocky walls at 15-35 m from the entrance.		Photo 5a: A diversified assemblage of sponges develops on the rocky walls and ceiling of the cave.		Photo 5b: Closeup view of the sponge Agelas oroides.

Photo 6a: Serpulid polychaetes colonize the rock walls of the inner part of the cave (35-50 m from the entrance).		Photo 6b: Closeup view of Serpulidae.		Photo 7: A dense population of the cerianthid Arachnanthus oligopodus on the soft bottom of the middle part of the cave.

From a morphological viewpoint, submerged caves of the Salento show a peculiar type of coralligenous speleothem (a complex biogenic substrate built by calcareous rhodophytes) which hangs from the ceiling in up to 1.2 m long club stalactites (Photo 8). If is not know if these speleothems have a rocky core, or they are the result of a "trickling" organogenous formation.

Photo 8: Coralligenous stalactites in grotte Sas� from Belmonte video.

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