Geomorphological, sedimentological, and ecological characterization of marine caves from Capraia Island (Tremiti Archipelago, southern Adriatic Sea, Italy). An integrated approach

Marine caves are sites of great interest from geomorphological and ecological viewpoints due to their significant environmental variability, being located at the boundary between marine and terrestrial domains. Most of the Mediterranean marine caves resulted from karst phenomena which widely affected the carbonate landscapes. At Tremiti Archipelago (southern Adriatic Sea, Italy), the karst activity is widespread, determining, in combination with existing tectonic features and long-term geomorphological evolution, the presence of several marine caves, partly or completely submerged. Two of these marine caves, located at Cala Caffè and Cala Sorrentino (Capraia Island), were considered for a multidisciplinary study focused on their geomorphological, sedimentological, and ecological characterization. These submerged blind-ended caves, located between 19 and 25 m water depth, show morphologies clearly linked to the tectonic-karst geomorphological setting. Superficial sediment samples were analyzed to derive grain size distribution, total carbon and nitrogen, isotopic ratios, living and dead benthic foraminifers, and dead brachiopods; water parameters were also considered. Sediment distribution showed a similar trend in the two caves, with finer textures, higher organic content in the inner stations, and increased biogenic components. Foraminifers showed a faunal change from the outer to the inner sectors associated with the decreasing grain size and the increased organic matter. Differently, the distribution of brachiopods did not display evident patterns; the differences in absolute abundance between the two sites were mainly attributed to the entrance dimensions and the morphology of the two caves, which deeply affected light penetration. This integrated approach demonstrated that geoforms, due to karst and tectonic processes, create small-scale coastal geomorphological habitats, greatly increasing biodiversity.