Seasonality of shellgathering from δ18O analysis and the role of marine molluscs in Mesolithic coastal economies of Atlantic Europe

The role of marine molluscs in Mesolithic subsistence strategies has long been debated, with many studies suggesting that they were of minor significance, used during times of scarcity or as supplementary food sources. However, recent work has challenged this view. This study introduces new seasonal and sub-annual data derived from oxygen-isotope ratios (δ18Oshell) of Patella vulgata Linnaeus, 1758 and Phorcus lineatus (da Costa, 1778) at the archaeological shell midden sites of El Perro, Mazaculos II, Arenillas and El Toral III in the Cantabrian region (northern Iberia, Atlantic Europe). The results provide high-resolution data on the timing of mollusc shell collection for these species and sites over a time span of 4730 years. We compare these results with seasonality studies of terrestrial fauna and previous analyses of molluscs from other sites, and integrate them with other sources of the subsistence economy. We demonstrate that some mollusc harvesting took place in all seasons, with a greater concentration in certain ones, and that this seasonal concentration differed as between species and sites. We conclude that molluscs were part of a coordinated strategy that systematically targeted different species according to their optimal food yield and according to seasons when other food resources were in shorter supply, making a substantial contribution to the viability of the overall palaeoeconomy. The coastal region as a whole was the focus of year-round settlement, but with the use of different sites in different seasons or for different functions, and evidence of extensive movement of individuals between coast and interior.