An ecotoxicological protocol with caged mussels, Mytilus galloprovincialis, for monitoring the impact of an offshore platform in the Adriatic Sea

An ecotoxicological protocol with caged mussels, Mytilus galloprovincialis, was developed to evaluate the potential impact of an offshore gas platform in the central Adriatic Sea. Reference organisms were collected on a seasonal basis from an unpolluted site and transplanted for four weeks in both the sampling area and to the investigated platform. Chemical analyses of trace metals in mussel tissues were integrated with a multi-biomarker approach for the early detection of biological responses at several cellular targets. Induction of metallothioneins, peroxisomal proliferation and activity of acetylcholinesterase were measured as markers for specific classes of chemicals. Special attention was given to oxyradical metabolism and appearance of oxidative-mediated toxicity to reveal a more general onset of cellular disturbance. In addition to individual antioxidants (superoxide dismutase, catalase, glutathione S-transferases, glutathione reductase, Se-dependent and Se-independent glutathione peroxidases, and levels of total glutathione), the total oxyradical scavenging capacity (TOSC) allowed a quantification of the overall capability to neutralize specific forms of intracellular reactive oxygen species (ROS; i.e. peroxyl and hydroxyl radicals). Cellular damages were evaluated as lysosomal destabilization (membrane stability, accumulation of lipofuscin and neutral lipids), lipid peroxidation products (malondialdehyde) and DNA integrity (strand breaks and micronuclei); the air survival test was finally applied to evaluate the overall physiological condition of mussels. Concentration of trace metals (As, Ba, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Zn) revealed only limited variations in transplanted mussels during various experimental periods and such changes appeared partly related to natural fluctuations. Among biological responses, variations of antioxidants and lysosomal stability were confirmed as sensitive early warning signals for biological disturbance of both natural and anthropogenic origin. The presented protocol with caged mussels allowed marked biological effects caused by the investigated platform to be excluded, and represented a useful approach that is easy to extend for monitoring the impact of offshore activities in the Adriatic sea.     

Influence of winds and oceanographic conditions on the mucilage aggregation in the Northern Adriatic Sea in 2003–2006

Meteorological and oceanographic conditions in the Northern Adriatic Sea in a year notable for massive mucilage formation (2004) were compared with those in years where this phenomenon did not occur (2003, 2005 and 2006) to suggest possible links. The months preceding the mucilage event in 2004 were considered the ‘incubation period’ and were characterized by a strong freshet in May which increased the water column stability. Winter cooling and scarcity of freshwater inputs from the Po River triggered the dense water formation and intrusion in the northern basin. Weak southeasterly winds and an increase in surface seawater temperatures contributed to maintain and reinforce the water column stability, and at the same time an intense diatom spring bloom created the conditions for accumulation of organic matter. The interplay of climatological forcings and biological processes caused temporal variations of dissolved organic carbon (DOC) and particulate organic carbon (POC) in the basin, with POC playing an important role in the aggregation process, as suggested by its increase relative to DOC before massive mucilage formation. We therefore suggest that high POC/total particulate nitrogen ratios in the suspended particulate organic fraction, a steep increase of POC/Chlorphyll a, and the decreased DOC/POC ratios represent ‘early warning’ signals of the main processes that lead to mucilage events in the Northern Adriatic Sea.