Mytilus galloprovincialis shell growth – Insights from shell geochemistry

Despite the wide geographic distribution of mussels and their importance in fisheries and aquaculture, understanding of temporal and spatial variations of their growth is still limited. This can be, at least partly, attributed to the lack of distinct growth lines in their shells. Our study uses geochemical properties of shells, particularly oxygen (δ18Oshell) and carbon (δ13Cshell) stable isotope values, to reconstruct mussel growth. Mytilus galloprovincialis specimens were collected from two of the most important bivalve aquaculture sites in the eastern Adriatic - Krka River estuary and Mali Ston Bay. The first site has variable environmental conditions, influenced mainly by the Krka River, resulting in a strong temperature and salinity gradient along the estuary. In contrast, Mali Ston Bay is a relatively shallow enclosed bay with more stable conditions. Samples for δ18Oshell and δ13Cshell analysis were acquired by manual microdrilling cross-sectioned shells from three similar sized shells from each site. In addition, analysis of elemental profiles (Mg/Ca, Sr/Ca, and Ba/Ca) in shells from the Krka River estuary was conducted using laser ablation ICPMS. Temperature and salinity values were obtained for each site through research and monitoring projects and used to calculate predicted δ18Oshell values. By aligning the measured δ18Oshell data along the predicted δ18Oshell curve, it was possible to reconstruct the timing and rate of seasonal shell growth. Results show that M. galloprovincialis shell deposition slows down and/or ceases during high temperature and low salinity periods. Specimens from the Krka River estuary had faster shell growth rates and were characterised by higher δ13Cshell values. Mg/Ca profiles of M. galloprovincialis specimens from the Krka River estuary, confirm growth periodicity data obtained by δ18O analysis. Ba/Ca peaks were also discussed by comparison with δ13C time-series and environmental data. Results have potential applications in fisheries studies as well as in palaeoecology and palaeoceanography research. •M. galloprovincialis is a high-resolution archive of δ18Oshell and δ13Cshell data.•Shell deposition slows down and/or ceases during high temperature and low salinity.•Spatial variations in M. galloprovincialis shell growth and δ13Cshell values.•Synchronised Ba/Cashell peaks in specimens from Krka River estuary.