INFLUENCE OF FLUID EMISSIONS ON SHALLOW-WATER BENTHIC HABITATS OF THE PONTINE ARCHIPELAGO (TYRRHENIAN SEA, ITALY).

An active fluid emission area located off the eastern coast of Zannone Island (western Pontine Archipelago) has been studied in order to investigate benthic assemblages related to vent-activity. The fluid escape feature is a giant depression (about 0.5 km2) located on the outer shelf, between 110 and 130 m water depth. Evidence of active emissions were detected by ROV observations and sediment sampling, whereas integration of high-resolution multibeam bathymetry, backscatter and ground-truth data allowed us to characterize and identify different seafloor types (e.g., lithified seafloor and sandy sediment). Moreover, the analysis of ROV videos and grab samples allowed the definition of the benthic assemblages (micro and megafauna) living within the vent-areas and in the nearby seafloor. This study shows results from the first integrated analysis of the morpho-acoustic, sedimentological and biological characteristics of the northern sector of the Zannone giant depression, highlighting great differences between vent and non-vent seafloor areas. In vent areas, the seafloor is characterized by high morphological complexity and peculiar benthic habitats strongly controlled by dissolution processes, indicating "extreme" conditions due to active fluid emissions.