Effects of pollution on the scope for growth of mussels (Mytilus galloprovincialis) from the Venice Lagoon, Italy

Mussels (Mytilus galloprovincialis) were sampled from six sites in the Venice Lagoon in May 1993 for measurement of their physiological responses (clearance rate, absorption efficiency and respiration rate) under standard laboratory conditions. Scope for growth (SFG) calculated for a ‘standardised ration level’ (0.4 mg particulate organic matter l−1) reflected the underlying pollution induced stress caused by the toxicants accumulated in the body tissues. Mussels from Chioggia had the highest SFG (16 J g−1 h−1) with slightly lower rates at Lio Grande, Crevan and Alberoni (9–10 J g−1 h−1), whereas mussels from the inner part of the lagoon (Salute and Canale Vittorio Emanuele) had significantly reduced SFG values (2 and −4 J g−1 h−1) which indicated severe pollution induced stress. There were significant negative correlations between SFG and the tissue concentrations of petroleum hydrocarbons, PCBs, DDT and HCH, but there were no significant correlations between SFG and the tissue concentrations of metals (Cd, Co, Cr, Cu, Fe, Hg, Mn, Fe, Ni, Pb and Zn). SFG was also calculated on the basis of measured POM levels prevailing at each site and this demonstrated that the inhibitory effects of toxicants on the growth of mussels living in the more polluted inner sites may be partially offset by the positive effects of eutrophication and the higher food/ration levels at these sites. There were also differences in the physiological responses and SFG of mussels from the two main cultivation sites within the Venice Lagoon (i.e. Alberoni < Chioggia) and these reflected the higher contaminant levels and lower food levels at Alberoni.