Comparison of biomarker responses in Ruditapes philippinarum from seaward and landward sites in the Lagoon of Venice

A multibiomarker approach was used to assess effects of different environmental conditions in the clam Ruditapes philippinarum from the Lagoon of Venice. Bivalves were monthly (March 2009-February 2010) collected in two sites of the Lagoon differently influenced by both anthropogenic impact and natural conditions: a seaward site (Punta Sabbioni, PS) located near the lagoon inlet of Lido and influenced by intense passage of ships, and a landward site (Canale Dese, CD) influenced by both riverine inputs and agricultural waste waters. Water temperature, pH and salinity values were recorded, and chlorophyll a concentrations and sediment grain size and organic matter content were determined at the two sampling sites. The following biomarkers were measured at both cellular/tissue and organism level: total haemocyte count (THC), endocytotic and haemolymph lysozyme activities, gill acetylcholinesterase (AChE) activity, condition index (CI) and survival-in-air. Although a similar pattern of variation in THC values was observed at the two sites, THC was generally lower in clams from CD. From April to July, clams from PS showed a significantly higher endocytotic activity, whereas lysozyme activity was generally (8 out of 10 months) lower at PS. Clams from CD showed a reduced AChE activity in most samplings. As for the CI, it was significantly higher in PS clams in April, May, June, January and February. Lastly, the resistance to air exposure of clams from CD was shown to increase significantly with respect to that of animals from PS in 7 out of 10 months. Immunomarker responses highlighted an overall better condition for clams from PS and suggested a reduced immunosurveillance in clams from CD. The lower AChE activity recorded in clams collected at CD indicated a possible exposure of bivalves to neurotoxic compounds due to drainage waters from agricultural land. Interestingly, a different response was provided by the two biomarkers measured at organism level, CI increasing and survival-in-air decreasing in PS clams. Overall, the present study promotes the use of a multibiomarker approach in assessing ecological quality in estuarine systems worldwide.