A key to seasonal shellfish exploitation: Elemental mapping of Mg/Ca ratios in Lutruwita (Tasmania) Cellana limpets
The littoral environment has considerable influence on life history traits and patterns of growth in marine molluscs due to changes in water temperature, oxygen levels and nutrient availability. The outer shell that protects the soft bodied invertebrate is laid down in individual growth increments, which contain biogeochemical signatures related to seasonal fluctuations and annual variations in the animal's immediate environment. On Lutruwita (Tasmania) coastlines, shellfish was a dependable food resource of past Pakana/Palawa (northern/southern Tasmanian Aboriginal peoples') through variable climatic regimes of the Holocene epoch. The durability of mollusc shell in depositional sediments makes them one of the most ubiquitous materials in archaeological sites that can provide valuable archives on the season of human consumption, subsistence strategies, and palaeoclimatic history. Yet, the ability to test large samples for robust biogeochemical interpretations using oxygen isotope analysis (δ18Ο) can be restrictive due to limitations of time and finances. Recent developments in Laser Induced Breakdown Spectroscopy (LIBS) offer an affordable, rapid and minimally invasive technique in screening zooarchaeological shell assemblages for variations in their temperature records over time. In our study, initial testing of modern Lutruwita gastropods using LIBS to map elemental Mg/Ca intensity ratios in Cellana solida (Blainville, 1825) produced promising results consistent with other limpet sclerochronology studies. Oxygen isotope measurements were used to calibrate LIBS results and interpret parallel changes in Sea-surface Temperature (SST) to develop a model on the season of collection in the modern samples. Results revealed high-resolution records of SST variability and seasonal limpet feeding patterns. This indicates that C. solida holds great potential for investigating past marine economies and land use patterns.
