Seashells in situ on Swansea Bay strandlines or drift lines are mostly tiny immature common cockle shells but there are many other species of bivalve and gastropod mollusc shells too. I noticed mussels, tellins, and oysters, winkles, top shells, netted whelks, sting winkles, slipper and common limpets, and I am sure there were many more types. There were seven drift lines of shells lying parallel to the water line and decreasing in the number of accumulated shells sequentially up the shore. Each line represents the highest reach of the sea on a series of subsequent falling tides that were decreasing in reach each time.
It was interesting to see that wave-worn pieces of black coal and dark clinker from industrial plants across the bay were scattered amongst the light coloured shells together with a fair number of burial-blackened periwinkles. Many of the shells were fragmented and the accumulations included the calcareous tubes of marine worms. It would be lovely next time to take a sample home and sort it through under a binoc. I am sure that it would reveal much more information.
Click on any image below to see the details in a larger version.
The beautiful orange-yellow paired valves of a Banded Wedge Shell, Donax vittatus (Da Costa), lying like a butterfly on the beach at Rhossili Bay. It is one of the most common bivalved molluscs on this stretch of shore and there are lots of the empty shells of this type on the strand line. They exhibit a range of colours and sometimes the inside of the shell is tinted a wonderful purple.
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.
Some of the things that caught my eye as I walked along the beach at Studland in Dorset, England, included interesting beach stones; stranded clumps of red, green, and brown seaweeds; an empty shell of a clam just eaten by a bird; and tubes of Sand Mason Worms.
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 contentsand a copy of the application form as pdf files.
The shingle shore at Whitstable in Kent is protected by massive wooden groynes or breakwaters. At the time of my visit, the tide was high and the flint and other mostly worm-holed pebbles were steeply banked. The flat top of the beach was stabilised by vegetation with pink and white valerian and yellow ragwort the most colourful flowers. Pale bands of white empty oyster shells (mostly the rock oyster Crassostrea gigas) were high, dry, and dull on the shingle between the groynes; while lower down splashed by waves or heaped up against the wooden sea defence structures was a great variety of other empty shells including winkles, cockles, mussels, limpets, slipper limpets, whelks, netted whelks, Manila clams, and sting winkles. These were jumbled up with wet and dry seaweed, horn wrack, small pieces of driftwood, and flotsam. There was a marked contrast in the appearance of the shells and stones between the water’s edge where the wet shells were brighter and more colourful and the upper shore where everything was dry.