Crassostrea and TBT – a very thick shell

Posted on August 21, 2017 by winderjssc

I been looking out some specimens of oyster shells that I collected from modern oyster beds on the south coast of England in the early 1980s. Way back in the early to mid 20th century, the hulls of boats were often coated with anti-fouling paint containing Tri-butyl tin (TBT). It was discovered that seawater contaminated with this chemical had an affect on some marine invertebrates. One of the noticeable phenomena was the way its presence caused the shell layers and chambers of the imported Pacific oyster (Crassosrea gigas) to wildly proliferate. Shells do in fact thicken naturally with age anyway – but in shells affected by TBT the rate of thickening is abnormal. Ultimately this unusual thickening prevented the oyster from opening up its two shell valves to feed and thus caused death of the organism.

A lot of research has been done regarding the affects of TBT on oysters. Laws have been introduced banning the substance in anti-fouling paints. The specimen illustrated in this post (with the images showing the same shell from various perspectives) is probably a rare survivor from the era when such abnormalities were fairly common. Nowadays, proliferation in shell growth of this type is more likely to be caused naturally and not chemically induced.

Molluscs in Archaeology – new book announcement

Posted on May 24, 2017 by winderjssc

I am delighted to announce the forthcoming publication of a brilliant new book called Molluscs in Archaeology – methods, approaches and applications edited by Michael J. Allen and published as part of the Studying Scientific Archaeology Series (3) by Oxbow Books. I have myself contributed a chapter on Oysters in Archaeology to this book, summarising my past research and suggesting new ways forward using latest technologies. It is available at a pre-publication discounted price for a limited period. See the details below. You can also download a list of the contents and a copy of the application form as pdf files.

A Modern Oyster Shell Midden

Posted on May 14, 2017 by winderjssc

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.

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

Kiosk selling Whitstable oysters on the beach

Strings of oyster shells for use as cultch to catch oyster spat

Oyster cultivation equipment on the beach at Whitstable

The Royal Native Oyster Stores at Whitstable

Modern oyster shell midden by the Royal Native Oyster Stores in Whitstable

An Oyster Shell with a Black Pearl

Posted on January 27, 2016 by winderjssc

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)

Posted on October 3, 2013 by winderjssc

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

Wild Oysters on the Queensland Coast Part 2

Posted on April 22, 2013 by winderjssc

The oysters that I found on the rocks at the northern end of Three Mile Beach in Port Douglas were so different from the ones I had seen at Cape Tribulation that I wondered if they were oysters at all.

The identification of Rock Oysters of the Saccostrea Group in the Indo-West Pacific is a fairly hot topic and some very interesting work was completed a few years ago to try and sort out what is what. See the work of Katherine Lam and Brian Morton.

On the basis of shell morphology, I think the oysters illustrated in this post are Saccostrea mordax which are distinct from the other Saccostrea species in having regularly-spaced grooves radiating from the umbone to the ventral margin of the right valve, the triangular shell shape, and finely plicated valve margin (with regular m-shapes). The left valve is completely attached as in the other species of Saccostrea such as cucullata, glomerata, and kegaki which are all morphologically similar to each other with an oval, deeply cupped left valve and a smaller, relatively flat right valve with slightly plicate, raised margins.

The molecular study by Lam and Morton (2006), based on samples obtained from along the whole of the Australian coastline, clarifies what is known about rock oyster biogeography. The identification of the oysters shown here from Port Douglas tallies with the distribution of Saccostrea mordax that is now thought to have a range from the tropical eastern coast of Australia, along the northern coast and throughout Western Australia. S. glomerata only occurs on the south-eastern coast of Australia on temperate shores from southern Queensland to New South Wales while S. cucullata shares the geographical range of S. mordax. One exception, based on someone’s personal observation – and not as a result of inclusion in the mitochondrial DNA work – is that putative S. mordax also occurs, but in much lower numbers, on shores dominated by S. glomerata around Moreton Island and Sydney.

Wild Oysters on the Queensland Coast Part 1

Posted on April 20, 2013 by winderjssc

I have written a lot about the natural variations in oyster shells belonging to the British Native, Flat, or European Oyster, Ostrea edulis Linnaeus. However variable these shells may be, it is always possible to identify the shells as belonging to that species, and to distinguish them from other species.

In Australia and the Far East, the oysters that grow wild and naturally on the tropical shores include several species of Saccostrea which can be difficult to differentiate from one another because of the diversity of their outward appearance. The morphologies of Saccostrea glomerata, Saccostrea cucullata, Saccostrea kegaki, and Saccostrea mordax, are so variable and overlapping that is not always possible to tell them apart by eye. As with so many other groups of organism currently being investigated (marine algae for example), it is only by use of mitochondrial-DNA analysis that true identities and relationships can be established (Lam and Morton 2006).

Which brings me to a discussion of the Rock Oysters that I photographed in several locations on the Queensland Coast. The images shown in this Posting were taken at Cape Tribulation in tropical Far North Queensland. Just going by the external characteristics, I suggest that they may be Saccostrea glomerata – also called the Sydney Rock Oyster. However, the differentiation of that species from Saccostrea cucullata is so problematic at times even for experts that oysters like this are frequently given both names, S. glomerata cucculata.

In following Posts I’ll show oysters growing in Yawarra Bay, Trinity Bay, and Port Douglas for comparison with these from Cape Tribulation. The shells from the rocks at the northern end of Three Mile Bay at Port Douglas look very different from the others and I think that they may be Saccostrea mordax. I’ll also refer in more detail to the Lam and Morton paper:

Lam, K. and Morton B. (2006) Morphological and mitochondrial-DNA analysis of Indo-West Pacific Rock Oysters (Ostreidae: Saccostrea species), Journal of Molluscan Studies (2006) 72: 235 -245, Oxford University Press on behalf of The Malacological Society of London.

Stories that old oyster shells tell – part 8

Posted on June 13, 2010 by winderjssc

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.

Stories that old oyster shells tell – part 7

Posted on June 12, 2010 by winderjssc

The following is the seventh 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 7

THE GENERAL PICTURE

Oyster and other marine mollusc shells have been examined from 60 sites for this project. In addition to firmer ideas about movements of oysters between different localities in the past, and site specific information about oyster usage, in broad and brief terms, the following picture emerges about oyster exploitation in Britain.

No oyster shells seem to have been recovered from Iron Age sites. Specimens found at Owslebury in Hampshire are now believed to be incorrectly dated to that period.

Roman sites throughout the UK are renowned for the massive quantities of oysters. Contrary to assertions in the literature, no physical or documentary evidence has been found so far to indicate that the Romans introduced oyster cultivation to Britain. Although they used cultivation techniques in Italy, these would have been impractical and unnecessary in Britain. Oysters appear to have been an unexploited resource immediately prior to the Roman invasion.

The claim that oysters were transported around Britain alive in lead tanks of salt water seems also to be highly unlikely and immensely impractical. Oysters will remain fresh for up to ten days if kept cool and packed closely to prevent opening of the valves. The transport system was excellent by road, river and sea. Oysters may have been packed tight inside British made pots that were marketed to the Romans – black burnished ware pottery manufactured on the southern shores of Poole Harbour in Dorset, adjacent to abundant natural oyster beds, was sent as far afield as Housesteads on Hadrian’s Wall.

The large average oyster size for the period may reflect an abundance of mature specimens, a preference for eating larger oyster meats than we select today, as well as a rapid growth rate.

Saxon sites also produce lots of oysters but these are mostly near the coast or with easy access by river to the coast. Deterioration of the roads with the exit of the invaders and poorer organisation meant that oysters could not be sent far. Average size is slightly but significantly smaller than those from Roman sites. To date there is still no evidence for farming or cultivation of oysters.

By the Medieval period, oysters were far more widely distributed across the country. They were also very noticeably smaller. Their size tended not to be the result of selecting less mature specimens but rather a much slower growth rate. This could be attributed to temperature changes but is also likely to be a direct result of oyster relaying and storage activities. Documentary records are made about the ownership of oyster beds and oyster fishing rights. Oysters that are re-laid inter-tidally and periodically exposed at low tides cease to grow whilst out of water. Simultaneously they learn to keep the valves tight shut when exposed to the air. This ability means that they stay alive for longer when traded and dispatched. Improved longevity in keeping fresh means that oysters can be sent greater distances. The greater numbers of oysters found on coastal sites reflects their easy availability and indicates that they were a staple of the diet. The smaller numbers of oysters found at inland sites suggests that the cost of transporting them made them an occasional and luxury item for these people.

Not many oyster specimens of Post-medieval date were made available for study, so conclusions are few. The shells were smaller than in earlier periods.

The Modern period, for current purposes, is taken as including the 19^th century onwards. This saw the advent of the railways and with them a cheap way of selling oysters to the masses all over the country. It was a boom time for oystermen and more and more boats went out to fish the beds. Holding pits on the shore became commonplace to store the catches before marketing. Prices of oysters plunged. They became the food of the common people everywhere, not just those living on the coast. They were so cheap that London apprentices complained of their monotonous diet of oysters and salmon.

Eventually, the oyster beds were over-fished and stocks became depleted. Efforts were made to cultivate oysters and breed foreign species. All attempts failed. The final blow to the incredibly successful oyster industry of the 19^th and early 20^th centuries came with massive extinctions of beds in the 1920 – thought to result from extreme cold weather and disease.

A few natural beds of oysters survived. Oysters became a luxury item on the menu again. A second catastrophe in the form of Bonamia disease decimated remaining stocks in the 1970s. This time modern technology came to the rescue of the British oyster industry by breeding oyster spat of both Ostrea edulis and Crassostrea gigas in the laboratory so that beds could be restocked. Oyster farming today with its net bags of brood oysters and floating platforms would not be recognised by our predecessors. Their methods were undoubtedly simpler but harder and we still have much to find out about them.

In the next and final part of this brief summary of the research I’ve carried out on oyster shells from archaeological deposits over an extended period of time, Part 8, looks at possibilities for future studies of this subject and provides a selection of references of work cited in this account.

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.

Stories that old oyster shells tell – part 6

Posted on June 11, 2010 by winderjssc

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.

Jessica's Nature Blog

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Category Archives: Oyster Variations

Crassostrea and TBT – a very thick shell

Molluscs in Archaeology – new book announcement

A Modern Oyster Shell Midden

An Oyster Shell with a Black Pearl

Oyster Shells at Whiteford (25.07.13)

Wild Oysters on the Queensland Coast Part 2

Wild Oysters on the Queensland Coast Part 1

Stories that old oyster shells tell – part 8

Stories that old oyster shells tell – part 7

Stories that old oyster shells tell – part 6