Environmental Impact of Offshore Gas Activities on the Benthic Environment: A Case Study

Multidisciplinary monitoring of the impact of offshore gas platforms on northern and central Adriatic marine ecosystems has been conducted since 1998. Beginning in 2006, 4–5 year investigations spanning the period before, during, and after rig installation have explored the effects of its construction and presence on macrozoobenthic communities, sediment, water quality, pollutant bioaccumulation, and fish assemblages. In this study, sediment samples collected at increasing distance from an offshore gas platform before, during and after its construction were subjected to chemical analysis and assessment of benthic communities. Ecological indices were calculated to evaluate the ecological status of the area. Ecotoxicological analysis of sediment was performed to establish whether pollutants are transferred to biota. The study applied a before–after control-impact design to assess the effects of rig construction and presence and provide reference data on the possible impacts of any further expansion of the gas extraction industry in the already heavily exploited Adriatic Sea. Only some of the metals investigated (barium, chromium, cadmium, and zinc) showed a different spatial and/or temporal distribution that may be platform-related. In the early phases, the sediment concentrations of polycyclic aromatic hydrocarbons were below the detection limit at all sites; they then became detectable, but without significant spatial differences. The present findings suggest that the environmental effects of offshore gas platforms may be difficult to quantify, interpret, and generalize, because they are influenced by numerous, often local, abiotic, and biotic variables in different and unpredictable ways.