Stories that old oyster shells tell – part 2

Regular visitors to Jessica’s Nature Blog will no doubt have noticed the frequency with which photographs and articles are posted about the many variations to be seen in the shells of the British Native, Flat or European Oyster, Ostrea edulis Linnaeus. Variation in oyster shells has been a subject that has interested me for many years – mainly because of its implication for the understanding of this particular marine mollusc in archaeological contexts. You can see these previous oyster shell posts by clicking here for the Oyster Variations category.

The following is the second instalment of an 8 part summary of the work I have been undertaking on Flat Oyster shell specimens from archaeological and present day contexts.

  Two thousand years of eating oysters in the UK:

an archaeological perspective

Part 2

METHODS

Many of the distinguishing features found in the shells of fresh or live oysters may not survive burial conditions over hundreds of years. Most soft parts of the mollusc itself or the organisms attached to it are likely to be absent. Breakage, wear and erosion will have affected harder parts, smoothing the sculpturing or ornamentation and damaging adhering epibiont structures.

Whilst many excavated shells are worn and relatively featureless, some can remain surprisingly fresh in their appearance and even retain pigmentation and fragments of ligament and periostracum. Figure 1 that shows the similarity between an oyster washed up on the beach at Oxwich Bay, Gower in 2005 and a 12^th century shell recovered from an extensive midden on the edge of Poole Harbour in Dorset.

Figure 1 Natural colour banding in ancient and modern shells of the British Native Flat Oyster

The one thing that was abundantly clear from the examination of that first batch of oyster shells from Saxon Southampton (Winder 1980; Winder 1997) was that the size and shape varied considerably within the samples. And once the shells had been carefully washed, other features could be seen such as the remains of encrusting epibiont organisms like barnacles and Bryozoa, and damage caused by burrowing worms and sponges. The shells could be clumped together in groups. Miscellaneous debris – like pebbles or other marine mollusc shells – was frequently attached.

Man-made marks were noted such as V-shaped notches on the shell margin caused by opening the oyster and cut marks on the smooth inner surface where the meat had been scraped off. Descriptions of the different recorded features can be found in Winder 1993, Chapter 2 Structure and variation in oyster shells. A collage of some of these characters in oyster shells can be seen in Figure 2. For much more detailed pictures and descriptions of recordable features in oyster shells look at the posts in Jessica’s Nature Blog in the Oyster Variations category.

Figure 2 Examples of epibiont infestation and encrustation in shells of British Native Flat Oysters from archaeological excavations

A standard method has been devised for recording both the measurable and objective features as well as the subjective and descriptive characters of each oyster shell. (Winder 1993, Chapter 3 Demonstration of variability – the methods). Up to 25 features are recorded. The information can be collated and expressed as a mean frequency of occurrence of each characteristic in the whole sample. These frequencies give each sample a unique description. The samples can then be compared on an intrasite or intersite basis, between feature types, different areas of site, and different periods of occupation.

Before discussing some examples of the findings from analyses of this data, it is important to reflect, all be it briefly, upon the nature of the data being used, and the particular constraints that can arise when using archaeological material rather than recent samples over which there would be a greater level of control in selection.

So, in the next instalment, Part 3 will describe some of the caveats, warnings or potential difficulties, to bear in mind when analysing archaeological oyster shells.

N.B. Please leave a comment or e-mail me directly on winderjssc@aol.com if you would like to ask any questions or to have a free copy of the complete article sent to you as a pdf file. This article is just a very brief summary of my archaeological oyster research. A small selection of references to publications and reports is provided with the article.

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