SEASONAL-VARIATION OF TRACE-METAL CONCENTRATIONS IN THE DIGESTIVE GLAND OF THE MEDITERRANEAN MUSSEL MYTILUS-GALLOPROVINCIALIS - COMPARISON BETWEEN A POLLUTED AND A NON-POLLUTED SITE

Seasonal changes in metal (Cu, Fe, Mn, Pb, and Zn) concentrations were observed in the digestive gland of the Mediterranean mussel, Mytilus galloprovincialis, from both a polluted and a non-polluted population. Digestive gland of mussels from the polluted site showed metal concen trations appreciably higher than in non-polluted organisms, especially for Pb (up to 160 mu g/g d.w.), Mn (up to 300 mu g/g d.w.), and Fe (u p to 8,500 mu g/g d.w.), whereas the two populations showed maximum me an values, respectively, of 34 and 20 mu g/g d.w. for Cu and 170 and 1 20 mu g/g d.w. for Zn. Over 1 year (1991), differences between maximum and minimum values were moderate only in the unpolluted organisms. Du ring gametogenesis, while the metal concentrations (expressed as mu g/ g dry weight) decreased in the digestive gland, the tissue burden (as mu g) in that organ remained nearly constant or increased slightly. Th e apparent decrease in metal concentrations was probably due to the pe netration of gonadic tissues into the digestive gland during gametogen esis, which biologically diluted metal concentrations in mussels from both the polluted and unpolluted populations. The effect of mussel siz e on trace metal concentrations in the digestive gland was demonstrate d during different stages of the reproductive cycle. Higher concentrat ions were found in smaller organisms; however, during the spawning per iod, due to the fact that this is not a synchronous process within a p opulation, the organisms exhibit a high variability in digestive gland weight which can mask this relationship when digestive gland weight i s used as a size-index and as a parameter of the trace metal digestive gland burden.