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