THE RESPONSE OF LIVING FORAMINIFERAL ASSEMBLAGES TO HYDROTHERMAL VENT INFLUENCE: AN EXAMPLE FROM THE PONTINE ARCHIPELAGO (TYRRHENIAN SEA, ITALY)
The Western Pontine Archipelago, located about 30 km away from the Italian Peninsula, is composed of three volcanic islands (Ponza, Palmarola and Zannone).
The active fluid emissions have been discovered 3 km off the eastern sector of Zannone Island, in a water depth ranging between 105-130 m (outer continental shelf), and affect the Late Quaternary lowstand and highstand deposits. This area appears as a large depression of about 0.5 km2 (900 m long and 500 m wide) with an elongated shape.
Sediment, high resolution multibeam bathymetry, biological and video data were acquired in order to characterise both the morphological and biological features related to venting activity. Analysis of ROV videos and sediment sampling allowed us to define the specific living benthic communities within the large depression and among the surrounding seafloor. Great differences among the morphology, sedimentology and microfauna characters between vent and non-vent seafloor areas. As regard the micropaleontological analyses, all samples were stained with Rose Bengal to distinguish living and dead assemblages. Diversity index (α-Fisher index), Faunal density and Foraminiferal Abnormality Index (FAI) were calculated to define the structure of the assemblage and the degree of environmental stress. The benthic foraminiferal assemblages highlights the complete lack of both hyaline and porcelanaceous tests; this fact suggests the presence of strong dissolution processes whereas the patchiness distribution of agglutinant species suggests a direct relation between distribution and very local environmental conditions.