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.
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.
The sand on the Island of Herm, which is one of the Channel Islands, is mostly made of shells and shell fragments. A good place to examine the sand is Belvoir Bay where waves and currents wash shells ashore and break them up. The small cove lies at the foot of modest cliffs of Herm Granodiorite with xenoliths; and eroding rocky outcrops strew the shore at the base of the cliffs. Hollows and crevices in these rocks are filled with coarse shell sand containing many intact little shells of both bivalve and gastropod molluscs. Even minute sea urchin tests survive. I took a handful of the sand home to photograph against a scale, and compare them with some mature-size shells from the same beach and nearby Shell Beach. I have fond memories of visiting the island and collecting shells there forty years ago.
Most of the examples of this fossil bivalve, Ctenostreon proboscideum, were partial specimens embedded in the rocks at Ringstead Bay in Dorset, England. However, the large strongly-ribbed shell is unmistakable and easily recognised in the many boulders on the beach at the west end of the bay – at least they were easily seen when the pebbles had all been washed away after the storms. The photographs in the gallery above show Ctenostreon shells as they were found on the beach last week. The boulders had fallen from the Ringstead Coral Bed which is a narrow layer, packed with fossils, of no more than 30 centimetres depth, and which can be seen in short lengths in the vertical section through the strata at the top of the beach.
The almost complete fossil specimen shown with the blue background (photographed at home) was found many years ago after similar severe weather. You can see that the two valves are still together and the space between them filled with marly limestone material, indicating that the original animal was already dead, with the two shells gaping open, when it was buried under new sediments.
Strong winds dried the very top layer of the wet sand on Rhossili beach, lifted the grains just above the surface, and drove them with great ferocity across the vast expanse of shore. The gusts of sand-laden wind scoured the beach into contour patterns and left buried seashells stripped and exposed to windward. Beautiful, natural patterns were created.