Strengthening the evidence for seasonal intertidal exploitation in Mesolithic Europe and new insights into Early Holocene environmental conditions in the Bay of Biscay from the oxygen isotope composition of Phorcus lineatus (da Costa, 1778) shells

Marine molluscs have been exploited by human societies since prehistoric times. Such practices have often resulted in large accumulations of shell remains in archaeological sites that offer unique information on biological, ecological and cultural aspects of human interaction with coastal systems in the past. In this study, stable oxygen isotope (δ 18 O) analysis was carried out on archaeological shells of Phorcus lineatus (da Costa, 1778) from the Mesolithic shell midden site of J3 (northern Iberian coast) to determine the seasonality of intertidal collection. The results indicate a consistent pattern of winter exploitation, supporting the emerging view that collections were governed by cost-benefit and management principles that are now widespread documented in other coastal Mesolithic sites in Europe. The consistent seasonal collections of P. lineatus during colder months can be taken as evidence of specie-specific management strategy to optimize yield while preserving local populations for future exploitation. Our results reinforce the view that European hunter-gatherers developed ecological knowledge on specific animal resources that persisted over large geographic areas. Additionally, from a palaeoenvironmental perspective, the sea surface temperatures (SST) inferred from δ 18 O values derived from mollusc shells (SST δ18O ) indicate that coastal marine waters during the Early Holocene in the southern Bay of Biscay were warmer than those observed today. These environmental conditions are evaluated in relation to changes in insolation and ocean currents over time. • New evidence continues to support that European Mesolithic populations preferentially exploited littoral resources during colder months. • Seasonal resource exploitation developed by prehistoric foragers was strategically designed to maximise energetic returns. • Multi-site dataset suggests greater homogeneity between eastern and western Mesolithic subsistence strategies on the N Iberia. • Sea surface temperatures were slightly warmer than they are today due to changes in insolation and ocean currents over time.