SEDIMENT FEATURES AND FORAMINIFERAL ASSEMBLAGES IN THE FICARELLA CAVE (SAN VITO LO CAPO, SICILY, ITALY)

The submerged and partially submerged marine caves are protected in the framework of the EU Habitats Directive because they are peculiar environments from a geological and geomorphological point of view and as biodiversity hotspots. However, while the hard-bottom communities are relatively well-studied, only recently, their sediments’ chemical and physical characteristics, associated with their microfaunal content (benthic foraminifera), have been focused on. A project started in 2013 aimed at characterizing the Mediterranean marine caves concerning these aspects, with results applicable in protecting and conserving these environments and studying large-scale environmental changes. In this context, the sediments of the Ficarella cave were analyzed to identify different ecozones inside the cave and verify the supply of organic matter and microplastics. The cave, which is located on the eastern side of the San Vito Lo Capo peninsula (North-western Sicily), is constituted by the dolostones, limestones, and dolomitic limestones of the Panormide domain (Upper Triassic - Lower Cretaceous), densely affected by normal faults, mainly with NW-SE direction. Coastal gravity and karst landforms such as dolines, canyons, and caves testify to the interaction between Quaternary tectonics and climate change. Divers surveyed the cave to reference the sampling station in the environment and define the cave morphology. The entrance of the cave is at about 23 m depth, and it's wide with a sea bottom mainly characterized by sandy sediments; moving towards the inner the cave changes morphology with many fallen boulders, the depth decreases until very shallow depth, the upper part of the cave is emerged, and there is evidence of freshwater input. Along the existing mainline were positioned, starting from the entrance, 10 sampling stations at 10 m distance each, but only on 5 stations was possible sampling because of the presence of rocky outcrops in the others. Divers manually collected distinct aliquots of surface (0-2 cm) sediment for the analysis of grain size, organic geochemistry, microplastics, and benthic foraminifera (rose Bengal stained), while water parameters (temperature, salinity, and dissolved oxygen) were recorded using a multiparametric probe. Analyses of abiotic parameters and microplastic contents in sediments and organisms are still in progress, while preliminary results of the quantitative analyses of foraminiferal assemblages are available. Benthic foraminifera were found in the whole cave, with exceptional diversity (107 and 39 species in the dead and living assemblage, respectively), and a clear gradient with the distance from the entrance was recognized in the species distribution. The increase of typical species of Mediterranean marine caves was evident, while typically, marine species of hard and/or vegetated bottoms sharply decreased in the innermost cave. The presence of symbiont-bearing taxa up to the middle of the cave pointed to enough light for photosynthesis. This study represents a further step in studying the cave ecozones and their application to studies related to the environmental changes occurring rapidly in the Mediterranean basin.