Scanning life histories of stone age oysters

Lay summary authored by Niklas Hausmann. Read the full paper here:

Oysters are some of the most commonly eaten marine molluscs in the world.
This is true today and has been true for thousands of years.
During their history as reliable food source, oyster populations had ups and downs, and in Europe there were times when Oysters were eaten in the billions each year (Londoners alone ate 700 million per year in 1864), with dramatic effects on their overall number and life expectancy.

The European Oyster has not recovered from these times at all and currently, researchers as well as industrial fisheries are trying to build up sustainable population sizes again.
The problem with this large-scale endeavour is that we currently have only limited knowledge what such a population would look like in terms of its demography, life expectancy, or individual growth.
And to solve this problem, researchers are looking at archaeological sites from the Stone Age and during periods before any large-scale oyster exploitation. By looking at the ages, sizes and growth rates of these archaeological oysters, we can get a baseline, or reference, to which modern populations can be compared to.

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Elemental map and growth micro-image of the oyster shell thin section. The scale shown for the elemental map is also applicable to the mico-images. Note that the colouring of the elemental maps is based on the individual limits of each specimen’s Mg/Ca ratio, with bright colours showing high ratios and dark colours showing low ratios. Credit: N. Hausmann.

Our article, presents a new way of determining archaeological oyster ages in a very quick and inexpensive way, so that we can access this information in many places around Europe and throughout time.
Our new method is called elemental mapping through Laser Induced Breakdown Spectroscopy (LIBS), which is measuring geochemical changes in the different growth lines of the mollusc shell. The geochemical composition of those segments change depending on the environment and the animal specific internal processes. For instance, in the oysters, we expect the concentration of Magnesium to increase with higher growth rates. With most Northern European oysters stopping their growth during winter, we can use these repeating increases (and decreases) to reconstruct how many winters the animal lived through (i.e. their age in years).

Getting this kind of information is usually done via microscopic analysis of very thin slices of shell, which take a lot of time to make, or through other geochemical analyses using oxygen isotopes, which cost a lot of money.
So with our pilot study, we successfully explored the use of LIBS as a new, fast, and cost-effective way of looking at shells in the past, setting the way for regulating our current efforts of repopulating the overfished oyster regions of the North Sea.

Full paper: Hausmann, N., Robson, H.K. and Hunt, C., 2019. Annual Growth Patterns and Interspecimen Variability in Mg/Ca Records of Archaeological Ostrea edulis (European Oyster) from the Late Mesolithic Site of Conors Island. Open Quaternary, 5(1), p.9. DOI: http://doi.org/10.5334/oq.59
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