Stable oxygen isotope analysis of Phorcus lineatus (da Costa, 1778) as a proxy for foraging seasonality during the Mesolithic in northern Iberia

Abstract

The Mesolithic period in the Cantabrian region, a coastal area located in northern Spain, is characterised by a marked increase in the human use of coastal resources in comparison with previous periods, resulting in the formation of so-called "shell middens". Archaeological investigations have provided insights into the formation processes of these shell middens, as well as long-term changes in human exploitation of different marine resources and the relationship of foraging strategies to past climate changes. However, efforts to reconstruct the key environmental factor governing coastal subsistence and foraging resilience, the seasonal availability and use of different marine resources, have been limited in the region and, indeed, across coastal Mesolithic Europe more widely. Here, we use stable oxygen isotope analysis of Phorcus lineatus (da Costa, 1778), one of the most widespread molluscs in northern Iberian mesolithic coastal sites, in order to determine the season in which humans collected key coastal resources at the site of EL Mazo (Llanes, Asturias). We demonstrate that P. lineatus was exclusively collected in late autumn, winter and early spring. An experimental programme, in which modern P. lineatus specimens were collected in situ over the course of three years, established that relative meat yield varied within this species throughout the annual cycle, with higher relative meat yield during colder months. We argue that mollusc collection patterns were driven by a cost-benefit principle during the Mesolithic in the Cantabrian region and human populations had intimate knowledge of the seasonal developmental cycles of exploited marine taxa. This also highlights the importance of developing intra-annual records of resource use and climate change if coastal foraging is to be properly understood in prehistory.