Impact of the seasonal changes of the mussel digestive gland mass on the cytosolic metal and metallothionein concentrations

Abstract

Mediterranean mussels (Mytilus galloprovincialis) are abundant sentinel species commonly used for the assessment of the metal contamination of the coastal marine areas. Digestive gland, as a main metabolic and storage tissue, is often selected for metal and metallothionein (MT) determination. Although the induction of MT is regarded as a biochemical response to metal exposure, it is often reported that biotic and abiotic factors (e.g. food abundance, reproductive status, temperature, salinity) additionally influence MT levels. The aim of our study was to estimate exposure of mussels to metals by means of MT level, using the caged mussels deployed over 12 months in the “ hot spot” area of the Kastela Bay (Dalmatia, Croatia). The results were evaluated following the recommendations of the MED POL Programme. Observed spring increase of the digestive gland mass caused the “ biological dilution” of metal and MT concentrations, as the consequence of the growth of the gonadal tissue through the digestive gland. Thus, low concentrations of metal and MTs were observed during the gonad development stage. In order to assess MT and metal levels as the indicators of the metal exposure, additional parameters should be considered, e.g. the phase of the reproductive cycle and the digestive gland mass.