A Modern Oyster Shell Midden

Oyster shells in a heap at Whitstable for use as cultch for collecting oyster spat

I have spent a large part of my life studying oyster shells that have been excavated on archaeological excavations of sites in the British Isles dating from the last two thousand years. The shells have been found in a variety of contexts including middens which are heaps of kitchen waste including oyster and other marine mollusc shells. Strangely, I had never seen a modern equivalent until this week when I visited Whitstable on the north Kent coast. I had read all about the famous Whitstable Oyster Fishery but somehow had never got around to visiting the place.

I did not choose a very good day to see Whitstable for the first time. It was very cold, dull, and windy with the choppy sea high up the shingle beach and salt spray continuously misting my camera lens. Nonetheless, I had a great time and made some interesting discoveries – not least of which was my desire to go back ago and explore some more.

Almost the first thing I saw when I hit the shore after a coffee at the Horsebridge Gallery, was the building of the historic Royal Native Oyster Stores belonging to the Whitstable Oyster Company. It included a seafood restaurant closed at the time, and outside were two substantial heaps of empty oyster shells – middens – one against a wall and the other on the shore. A casual observer might wonder why mounds of empty shells had been left lying around and not properly disposed of. There is a good and logical reason.

The shells are being kept for cultch. The youngest form of an oyster is a free-swimming larval stage which needs to find somewhere suitable to settle down and grow. It is very particular about the type of object on which it will land and attach its embryonic shell. It has a limited time, maybe just a couple of weeks if the temperature is optimum, to find just the right place. It likes all sorts of hard substrates but it likes oyster shells best – sometimes empty ones and sometimes live ones.. Traditionally, this preference is catered for by the oyster fishermen who put down quantities of empty oyster shell as cultch on the seabed to encourage the settlement of young spat oysters. They also string old shells together to act as suspended spat catchers in the water. It is interesting to see these historic practices still in operation in an age when many oysters are bred in laboratories before being grown on in metal mesh bags on trestles covered by the tides. They use both old and new methods here.

The pictures in this post show more than one type of oyster shell. The Native British Oyster, also known as the European Flat Oyster (Ostrea edulis) is the type for which Whitstable is most famous. They also use the Pacific or Rock Oyster (Crassostrea gigas) which grows faster and is therefore a good commercial proposition, especially when in recent times the numbers of our native species have reduced.

An Oyster Shell with a Black Pearl

Oyster shell with attached pearl

I found this shell on Rhossili Beach. Oyster shells often wash ashore there. The European Flat Oyster used to grow in abundance around the Gower Peninsula in South Wales and was commercially fished until about the 1940’s when stocks declined to such an extent that it no longer remained a viable proposition. They are presently trying to re-introduce the oyster fishery.

Fresh shells brought up by the tide would seem to indicate that Ostrea edulis still lives and breeds in the locality. The older shells have evidence that they have been around for a long time, possibly decades. Many are very thick showing that they lived for a long time. Commercially fished or cultivated oysters are usually cropped at three or four years before the shell has achieved its maximum growth and are therefore relatively small and thin. Left undisturbed, O. edulis can live for fifteen years or more. However, after a certain time, the diameter of the shell more or less ceases to increase and the animal’s energy is concentrated on thickening rather than widening the shell.

The longer the oyster lives, the greater the possibility of its shell assuming unusual shapes and abberations. Some of the mis-shapes result from the animal’s defensive reaction to infesting or encrusting organisms on or in the protective shell. Occasionally, irritation of the fleshy interior by foreign objects causes changes in the way the shell is laid down by the internal nacreous layer. This is the way pearls are formed. You may be surprised to learn that commercially fished pearls, and cultivated pearls, do not actually come from oysters. The Pearl “Oyster” – is a mis-nomer. It is in fact a Pearl Mussel. The Latin name for the Pearl Oyster species (of which there are several) is Pinctada. and the species belongs to the Family Pteriidae a close relative of the true oysters – the Ostreiidae. When Julius Ceasar came to Britain with the invasion and extolled the beauty of British pearls, which he then exploited and exported back to Rome, he was referring to pearls from freshwater mussels Margaritifera margaritifera (Linnaeus).

It is not common to find pearls in true oysters like Ostrea edulis but they do occur. They are not considered to be as valuable as those from mussels and in some cases are prone to disintegrate with time. I have seen good examples in the museum at Colchester, Essex, which is an area reknowned for its oyster fishing industry dating back to at least Roman times.

Pearls as we commonly know them usually form as distinct separate bodies within the fleshy mantle of the oyster. Occasionally, the pearls are attached to the inner nacreous layer of the shell. They can be attached by a short stalk. That is what we have here in this beach-combed oyster shell. The “pearl” is attached to the inner surface of the right valve of the shell next to the pale kidney-shaped adductor muscle scar. [The strong adductor muscle joins the two valves in life and is used to close the shell when necessary. The default position of the oyster is to have the valves open and apart and it is automatically kept in this position by the ligament at the umbonal or hinge end of the shell.] The black colour of the pearl and the shell itself is the result of spending a considerable time buried deep down in anaerobic sediments. Black oyster shells are common on Gower beaches.

Oyster Shells at Whiteford (25.07.13)

Oyster shell (Ostrea edulis Linnaeus) on the beach at Whiteford Sands

Click on the pictures to enlarge them and view the descriptions.

Oyster shell (Ostrea edulis Linnaeus) on the beach at Whiteford Sands

Oyster shell (Ostrea edulis Linnaeus) on the beach at Whiteford Sands

Oyster shell (Ostrea edulis Linnaeus) on the beach at Whiteford Sands

Oyster shell (Ostrea edulis Linnaeus) on the beach at Whiteford Sands

Oyster shell (Ostrea edulis Linnaeus) on the beach at Whiteford Sands

Oyster shell (Ostrea edulis Linnaeus) on the beach at Whiteford Sands

Oyster shell (Ostrea edulis Linnaeus) on the beach at Whiteford Sands

COPYRIGHT JESSICA WINDER 2013

All Rights Reserved

Oyster Thieves at Studland & Ringstead Bays

Picture of Oyster Thief seaweed, Colpomenia peregrina Sauvageau, at Ringstead Bay, Dorset, UK on the Jurassic Coast World Heritage Site (P1120589aBlog1) 

The disappearance of oysters from privately-owned relaid beds has been an all too frequent occurrence in both relatively recent and historical times. Mostly this would have been an act of poaching or stealing by unscrupulous individuals out to make quick money with minimal effort. Sometimes the vanishing oyster stocks were blamed on other more natural phenomena such as severe storm conditions or more mysterious agents such as the curious one photographed and described here.

When I first saw one of the strange green gelatinous bubbles shown above, I didn’t know what to make of it. I thought maybe it was an accidental form of that bobbly slimey weed you sometimes get on the surface of water in hot weather. I certainly didn’t think of it as being a particular species of seaweed – but I was wrong.

It is Colpomenia peregrina Sauvageau, a brown seaweed commonly called the Oyster Thief because the strange mythology that has arisen around it. It attaches to stones and shells in the sea. Frequently it grows on large shells like those of the common oyster. Usually the hollow sphere is intact. However, if the capsule is damaged, the plant may be filled with air when exposed at low tide. It can then act like a float when re-immersed, rising in the water, and floating away – still sometimes attached to lighter stones or shells, including live oysters. The ‘behaviour’ of this organism was therefore sometimes blamed for whisking  away the valuable oysters from relaid beds.  

The picture at the top of the post shows an Oyster Thief in perfect condition from Ringstead Bay. More usually I have found them squashed as in the pictures below from Studland where holidaymakers and horseriders have trodden on one.

Seaeweed picture: Oyster Thief seaweed, Colpomenia peregrina Sauvageau, washed ashore and trodden flat by a passer-by on the sandy beach at Studland Bay, Dorset, UK on the Jurassic Coast World Heritage Site (P1060820aBlog2)

Seaweed picture: Oyster Thief seaweed, Colpomenia peregrina Sauvageau, washed ashore and squashed flat by the footsteps of a passer-by on the sandy beach at Studland Bay, Dorset, UK on the Jurassic Coast World Heritage Site (P1060821aBlog3) 
 

Revision of a post first published 22 April 2009

COPYRIGHT JESSICA WINDER 2011

All rights reserved

Stories that old oyster shells tell – part 8

 

The following is the eighth & final instalment of an 8 part summary of the work I have been undertaking on British Native or European Flat Oyster shell specimens from archaeological and present day contexts. You can see previous posts about the shells of  Ostrea edulis Linnaeus by clicking here for the Oyster Variations category.

Two thousand years of eating oysters in the UK:

an archaeological perspective

Part 8

FUTURE WORK

Most of the research described in this article has been undertaken in a part-time capacity and with minimal funding. The opportunity now arises to consider how to carry this archaeomalacological work forward. The elementary nature of the preliminary analyses reflects an original requirement to devise methods that were easy to learn and replicate on a wider scale by on-site non-specialists as much as the constraints imposed by limitations of time, funding and technical expertise. Although a great deal of information has been gathered so far, the potential of this has not yet been fully realised. From today’s perspective, the gaps in the data, shortcomings of the analyses, and possible new directions for enquiry become evident.

One of the first steps might be to construct an Access database of all the information available. Then acquire more sample data to make the database more representative. Enlisting the collaboration of a statistician to help rework the data would be desirable. And it would be advantageous to consider the more sophisticated techniques available if funding can be found. These techniques might include Inductively Coupled Plasma Mass Spectrometry to see if the chemical constituents of shells from different locations varied. An attempt could be made to extract DNA from the surviving organic components. Extraction and identification of any pigments encapsulated in the crystals might shed light on changing diet of the oysters.

After working on oysters for over thirty years now, I remain as passionate about the subject as ever, fascinated by their variability and what this might mean for the interpretation of archaeological material and our understanding of both human exploitation of this marine resource and of our changing natural environment.

 

REFERENCES

Bell, A. (1921) British oysters past and present. Essex Naturalist (Stratford). 19, 183-221 and 300-2.

Horsey, I.P. and Winder, J.M. (1991) Late Saxon and Conquest period oyster middens at Poole, Dorset.  In Waterfront Archaeology, Proceedings of the third International conference, Bristol, 1988, (eds G.L. Good, R.H. Jones and M.W. Ponsford), 102-104.  CBA Research Report No. 74.

Winder, J.M. (1980) The Marine Mollusca.  In Excavation at Melbourne Street, Southampton, 1971-76 (ed. P. Holdsworth), 121-127.  Southampton Archaeological Research Committee, Report 1, CBA Report 33.

Winder, J.M. (1987)  A report on the marine molluscs from the excavations at 49-53 Moorgate and 72-73 Coleman Street,  Unpublished report for the Department of Urban Archaeology, Museum of London.

Winder, J.M. (1991) Marine Mollusca.  In Redeemed from the Heath – the archaeology of the Wytch Farm Oilfield (1987-90), (eds P.W. Cox and C.M. Hearne), 212-216.  Dorset Natural History and Archaeological Society Monograph Series No. 9 for BP Exploration and its partners in the Wytch Farm Development.

Winder, J.M. (1992) The Oysters.  In Excavations in Poole 1973-83, (ed. I.P. Horsey), 194-200.  Dorset Natural History and Archaeological Society Monograph Series No. 10.

Winder, J.M. (1993) A study of the variation in oyster shells from archaeological sites and a discussion of oyster exploitation.  PhD Thesis, University of Southampton, Department of Archaeology, Faculty of Arts.

Winder J.M. (1997) Oyster and other marine molluscs, in Excavations at Hamwic, Volume 2: excavations at Six Dials edited P. Andrews, Council for British Archaeology Research Report No. 109, 247.

Winder, J. M. (2000) Oysters and other marine shells from Elms Farm, Heybridge, Essex, Report for Essex County Council Field Archaeology Unit.

Winder J. M. (2002) Oysters and other marine mollusc shells from Great Wakering, Essex, Report for Essex County Council Field Archaeology Unit.

 

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. 

 

 © Jessica Winder and Jessica’s Nature Blog, 2009. Unauthorised use and/or duplication of this material, including both text and photographs, without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Jessica Winder and Jessica’s Nature Blog with appropriate and specific direction to the original content.

 Photographs in this blog are copyright property of Jessica Winder with all rights reserved

Stories that old oyster shells tell – part 6

 

The following is the sixth instalment of an 8 part summary of the work I have been undertaking on British Native or European Flat Oyster shell specimens from archaeological and present day contexts. You can see previous posts about the shells of  Ostrea edulis Linnaeus by clicking here for the Oyster Variations category.

 Two thousand years of eating oysters in the UK:

an archaeological perspective

Part 6

EXPLOITATION MODELS – THE EVIDENCE CONSIDERED AS A WHOLE

The combination of features, from size and shape to epibiont and man-made damage, provides not only a standardised way of describing a sample of shells by giving it a unique identifier but also supplies a means of addressing some of the questions posed by archaeologists regarding the point of origin of the shellfish and the mode of its exploitation. A series of theoretical models has been drawn up that identify which types of evidence from the shells are indicative of the different aspects of oyster bed location and level of exploitation (Winder 1993 Chapter 11 The conclusions and discussion: Levels of oyster exploitation pp 281- 304). These models bring together ideas about which combinations of features in archaeological oyster shells, associated species, and excavated material structures might be useful for interpretation.

Five theoretical exploitation models are described but in reality there would be a continuum of gradually intensifying activities from sporadic hand-collection from natural intertidal beds to full-scale commercial cultivation and marketing of oysters. Each element of data recorded from the oyster shells and the site can potentially contribute to our understanding of the particular type of environment in which they lived, and the level of effort involved in their exploitation. For example, infestation evidence could be used to suggest the locality of the bed, whether the bed was inter-tidal littoral or shallow sub-littoral, harder or softer substrate and also the degree of salinity. Size distributions may reflect growth rate, recruitment variability, selection preferences, and survival rates. The diagram in Figure 5 shows as an example Model 1 which is for sporadic hand collection from natural beds. 

FIGURE 5 

The conceptual models described above and comparisons of size and infestation have been used to interpret the data from archaeological oysters and suggest where and how this shellfish was exploited. What can we now say about eating oysters in the past based on this archaeological evidence? This research has started to give a clearer picture about the way people have exploited oysters over the last two thousand years in Great Britain, confirmed some ideas previously held, and refuted others. It is a developing methodology that will help answer some of the questions posed by archaeologists.

Next, Part 7 will finally pull together some of the conclusions that have been enabled by the application of the methods described earlier and the results obtained from the examination of over 30,000 old 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 will be provided with the article.

© Jessica Winder and Jessica’s Nature Blog, 2010. Unauthorised use and/or duplication of this material, including both text and photographs, without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Jessica Winder and Jessica’s Nature Blog with appropriate and specific direction to the original content.

 Photographs in this blog are copyright property of Jessica Winder with all rights reserved

Stories that old oyster shells tell – part 5

   

The following is the fifth instalment of an 8 part summary of the work I have been undertaking on British Native or European Flat Oyster shell specimens from archaeological and present day contexts. You can see previous posts about the shells of  Ostrea edulis Linnaeus by clicking here for the Oyster Variations category.

 

Two thousand years of eating oysters in the UK:

an archaeological perspective

Part 5

Infestation differences

Differences in the types of evidence for encrusting or infesting epibiont organisms in oyster shells closely relates to the natural conditions in which the oyster was growing – such as the depth of water, the substrate and the geographical location. Principal Component Analysis (PCA) was used initially to compare the sum total of all recorded characteristics of an oyster shell sample. However, PCA proved most useful in differentiating oysters from different regions based on the infestation characteristics (Winder 2002).

 

FIGURE 4 

Figure 4 gives the result of a PCA of infestation in Roman oyster samples and demonstrates regional differences. Each coloured symbol on the chart represents a sample from a named site. It is only necessary to note for present purposes that the chart shows samples segregated mainly into two groups. Those from Essex and Suffolk are grouped together on the left and those from Dorset, Hampshire and Wiltshire to the right. Samples denoted ‘Shir for The Shires excavation in Leicester, and ‘Pud’ from Pudding Lane in London are included in the grouping of samples known to have originated in East Anglia and indicating that oysters at these inland sites were obtained from that part of the country.

The same marked differentiation can be seen for PCAs for other periods as well. The organisms that seem primarily (but not exclusively) to account for this regional differentiation of oysters from the South Coast compared with the East Coast are polychaete worms of the Polydora genus. These worms leave characteristic burrows in the shells. Polydora ciliata (Johnston) seems to be ubiquitous while the larger species Polydora hoplura Claparède appears to be restricted to southern waters. PCA seems a promising approach for pinpointing the source of oyster samples and will be developed.

 

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 will be provided with the article.

© Jessica Winder and Jessica’s Nature Blog, 2010. Unauthorised use and/or duplication of this material, including both text and photographs, without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Jessica Winder and Jessica’s Nature Blog with appropriate and specific direction to the original content.

 Photographs in this blog are copyright property of Jessica Winder with all rights reserved

Stories that old oyster shells tell – part 4

 

The following is the fourth instalment of an 8 part summary of the work I have been undertaking on British Native or European Flat Oyster shell specimens from archaeological and present day contexts. You can see previous posts about the shells of  Ostrea edulis Linnaeus by clicking here for the Oyster Variations category.

Two thousand years of eating oysters in the UK:

an archaeological perspective

Part 4

A FEW RESULTS

Some results of the analyses of the two main contributors to variability in the shells of Ostrea edulis L. are presented here. These relate first to size and, in the following Part 5, evidence of infestation and encrustation by epibionts.

Size differences

The size of oyster shells recovered from ancient sites results from a combination of factors: natural environment, genetics, and human influence. Examining size can potentially help to distinguish, for example, between oysters originating from different localities or subject to varying fishing practices. Measurements of more than 30,000 oyster shells were used initially and comparisons between the samples made by parametric and non-parametric statistical tests for various categories of sample (Winder 1993 Chapter 9 Intersite variation in size of oyster shells). These categories included samples from different geographical regions, inland and coastal sites, urban and rural sites, and various historical periods.

 FIGURE 3

Comparisons of size for broadly defined historical periods reveal interesting variations in mean size between the Roman, Saxon, Medieval, Post-medieval and Modern oyster shells. This appears to indicate statistically significant temporal differences in the average size of oyster shells. Roman shells are largest but size decreases progressively through successive periods until a recovery to almost Roman dimensions in the Modern period. The data will be reworked using more sophisticated computer software and the much larger database that has been acquired since this analysis was first completed.

Figure 3 is just a simple bar chart representation of the differences in size of oyster shells through time based on the original analysis. There are two bars for each period and these indicate the overall size for left  (blue bar) and right (red bar) valves. The sizes of the two types of shell valves are always different even for the same individual oyster. The right flat valve is smaller than the left and sits somewhat within the shallow saucer shape formed by the left valve. The perimeter of the right valve in life frequently has a flexible new growth of shell that extends to meet the edge of the left shell. In right oyster shells recovered from archaeological excavations this fragile outer margin is absent.

The final bar of the above chart, which represents results for Modern oysters, lacks figures for right valves. The reason for this is that the majority of the measurements in this category were taken from fresh living specimens of oyster in which it was not possible to determine with accuracy the dimensions of the in situ, almost embedded, right shells. The maximum diameter dimensions of the entire oyster were recorded in living specimens. Right valve measurements of living oysters would not be directly comparable in every instance with right valves of archaeological specimens.

In the next instalment, Part 5 will discuss some of the results from analysis of infestation characteristics in 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 will be provided with the article.

© Jessica Winder and Jessica’s Nature Blog, 2010. Unauthorised use and/or duplication of this material, including both text and photographs, without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Jessica Winder and Jessica’s Nature Blog with appropriate and specific direction to the original content.

 Photographs in this blog are copyright property of Jessica Winder with all rights reserved

Stories that old oyster shells tell – part 3

The following is the third instalment of an 8 part summary of the work I have been undertaking on British Native or European Flat Oyster shell specimens from archaeological and present day contexts. You can see previous posts about the shells of  Ostrea edulis Linnaeus by clicking here for the Oyster Variations category.

 Two thousand years of eating oysters in the UK:

an archaeological perspective

Part 3

 

CAVEATS TO ANALYSES OF THE ARCHAEOLOGICAL DATA

There are many challenges to working with archaeological oyster shells. There are possible biases to the material that would affect the analysis and interpretation of the data. Among the questions we need to ask is how representative are the examined samples of the potentially available pool of archaeological oyster material?

In the case of the extensive Saxo-Norman oyster heaps on Poole waterfront (Winder 1992; Horsey and Winder 1991) and the nearby 12th century middens at Ower (Winder 1991)) on the southern shore of the Poole Harbour, neither are likely to have been permanent habitation sites. The shells excavated from these sites are thought to result from processing of the meats prior to marketing with the shells being discarded on the spot; so they would probably represent the entirety of the catch.

Whereas, on sites such as Elms Farm in Essex (Winder 2000) near to the head of the Blackwater estuary famed for its oyster beds, the smaller numbers of shells remaining on site from Roman and early Saxon phases may well indicate that the majority of the catch was being marketed in the shell. Oyster shells are very bulky and can present a disposal problem when fishing for and eating oysters is an important part of community life; so an alternative possibility to consider, is that the shells may have been recycled. They can, for example, be returned to the sea bed as cultch on which oyster spat can settle; used to fertilise (lime) the fields; used in the manufacture of lime; crushed for chicken feed, shell-tempered pottery, medicines and cosmetics; used as hardcore, for paths and yard surfaces; and used as mortar for stone work.

How representative are the shells from an individual site of the original incoming samples to that site – both in quality and quantity? Moorgate and Coleman Street excavations in London (Winder 1987) of 11-12th century domestic rubbish pits uncovered strikingly different shells in different pits. One contained poor quality oysters of very small and very large size, while the other had all the better quality shells of the optimal mid-size range. It is easy to see how erroneous conclusions could have been drawn if the specimens from only one pit had been selected for analysis.

Has there been an excavation bias with only the larger or intact shells being retained? We need to know the criteria for retrieval. And subsequently, what was the rationale for selecting samples for analysis? How much reliance can be placed on comparisons of archaeological oyster shells with samples of modern material from known locations? Comparisons of this sort would be very informative. However, there have been substantial losses of natural oyster beds in Great Britain, plus coastline and sea-level changes, and possible contamination of native oyster beds by interbreeding with imported oysters from home and abroad.

Finally, the taphonomic history of the shells, soil conditions and disposal methods will affect the chemical and mechanical wear on the shells. There is randomness to shell survival and recovery as well as to the process of shells being made available for study. All of these factors have to be considered and they place restraints on the interpretations based on the shells. Additionally, there can never be enough samples. With this awareness, the  analysis of the data was carried out.

In the next instalment, Part 4 will describe some of the results obtained from analyses of size and infestation characters in the 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 will be provided with the article.

© Jessica Winder and Jessica’s Nature Blog, 2010. Unauthorised use and/or duplication of this material, including both text and photographs, without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Jessica Winder and Jessica’s Nature Blog with appropriate and specific direction to the original content.

 Photographs in this blog are copyright property of Jessica Winder with all rights reserved

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 12th 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.

© Jessica Winder and Jessica’s Nature Blog, 2010. Unauthorised use and/or duplication of this material, including both text and photographs, without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Jessica Winder and Jessica’s Nature Blog with appropriate and specific direction to the original content.

 Photographs in this blog are copyright property of Jessica Winder with all rights reserved