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.

Assessment of seabed litter in the Northern and Central Adriatic Sea (Mediterranean) over six years.

Seabed debris is much less investigated in respect to the sea surface and shores due to sampling difficulties and costs. However, detecting marine benthic litter is fundamental for developing policies aimed at achieving the Good Environmental Status in European Seas by 2020, as requested by the Marine Strategy Framework Directive. This study estimates seafloor litter abundance, composition, spatial distribution and main sources in the North-Central Adriatic Sea (FAO GSA 17) over a six-year period (2011-2016) with 67 stations sampled per year, representing the longest data set for the basin. Litter items collected using a "rapido" trawl were classified in six major categories. The average density of the litter collected over six years was 102.66 ±â€¯41.91 kg/km2. The highest concentration of litter was found in stations close to the coast within 30 m depth with a mean weight of 142.90 ±â€¯27.20 kg/km2, while the lowest value was recorded between 30 and 50 m of depth (41.12 ±â€¯9.62 kg/km2). Plastic was dominant followed by metal and other litter materials. Lost fishing nets and mussel culture debris accounted for 50% of the overall plastic litter collected. These data and the systematic monitoring of marine litter provide useful information to implement necessary measures to manage marine litter and minimize this type of anthropogenic pollution in the Adriatic region.

Characterization of microplastic litter in the gastrointestinal tract of Solea solea from the Adriatic Sea.

Micro-plastic particles in the world's oceans represent a serious threat to both human health and marine ecosystems. Once released into the aquatic environment plastic litter is broken down to smaller pieces through photo-degradation and the physical actions of waves, wind, etc. The resulting particles may become so small that they are readily taken up by fish, crustaceans and mollusks. There is mounting evidence for the uptake of plastic particles by marine organisms that form part of the human food chain and this is driving urgent calls for further and deeper investigations into this pollution issue. The present study aimed at investigating for the first time the occurrence, amount, typology of microplastic litter in the gastrointestinal tract of Solea solea and its spatial distribution in the northern and central Adriatic Sea. This benthic flatfish was selected as it is a species of high commercial interest within the FAO GFCM (General Fisheries Commission for the Mediterranean) area 37 (Mediterranean and Black Sea) where around 15% of the overall global Solea solea production originates. The digestive tract contents of 533 individuals collected in fall during 2014 and 2015 from 60 sampling sites were examined for microplastics. These were recorded in 95% of sampled fish, with more than one microplastic item found in around 80% of the examined specimens. The most commonly found polymers were polyvinyl chloride, polypropylene, polyethylene, polyester, and polyamide, 72% as fragments and 28% as fibers. The mean number of ingested microplastics was 1.73 ± 0.05 items per fish in 2014 and 1.64 ± 0.1 in 2015. PVC and PA showed the highest densities in the northern Adriatic Sea, both inshore and off-shore while PE, PP and PET were more concentrated in coastal areas with the highest values offshore from the port of Rimini.

Trophic structure of polychaetes around an offshore gas platform.

The distribution of polychaetes associated with an offshore gas platform built on a muddy-sandy bottom in the northern Adriatic Sea was investigated with emphasis on their feeding structure. Polychaete species were collected at different distances from the rig using a Van Veen grab. Assessment of the polychaete community and trophic groups for impacts related to the presence of the platform demonstrated significantly different abundances at rising distances from the rig. The present findings highlight an effect of the rig on the spatial distribution of polychaete assemblages. Even though the effects of gas platforms on surrounding benthic communities have been investigated in the Adriatic Sea, no studies have addressed the distribution of polychaete trophic groups along a gradient based on distance from the rig.

Spatial pattern and weight of seabed marine litter in the northern and central Adriatic Sea.

The present study analyzes spatial distribution and typology of marine litter on the seabed in the FAO Geographical Sub-Area 17 (northern and central Adriatic Sea). Two surveys were conducted during fall 2011 and 2012 and 67 stations were sampled each year. Litter items were collected using the "rapido" trawl, a modified beam trawl commonly used by the Italian fishermen to catch flat fish and other benthic species. Marine litter in the catches was sorted and classified in 6 major categories (plastic, metal, glass, rubber, wood, other). Plastic litter was further subdivided in 3 sub-categories based on its source: fishing nets, aquaculture nets and other. Plastic was dominant in terms of weight followed by metal and other categories. The highest concentration of litter was found close to the coast likely as a consequence of high coastal urbanization, river inflow and extensive navigation associated with the morphological and hydrological features of the basin.

Offshore platforms: comparison of five benthic indicators for assessing the macrozoobenthic stress levels.

Within the European Water Framework Directive, many studies have been conducted to evaluate the sensitivity/robustness of a variety of indices in relation to natural or anthropogenic disturbance events. However, these indices have rarely been applied to verify the impacts of disturbances in offshore environments, though the Marine Strategy Framework Directive recommends their use for assessing benthic community conditions and functionality. The aim of this paper was to determine which biotic indicator performed the best for detecting the impacts of offshore structures on benthic populations in the Adriatic Sea. The impacts of four rigs were investigated six months after their installation, and the H', AMBI, m-AMBI, BENTIX, and BOPA indices were assessed. Although these five indices delivered some contradictory results because of the differences in their structure and discrepancies in their assignment of species sensitivity, the BENTIX, H' and BOPA indices appear to evaluate stress levels better than the AMBI and m-AMBI indices, which tend to provide results that are slightly overly optimistic.