Strandline Shells on Swansea Bay

Seashells on the beach at Swansea Bay

Shells drift lines on the beachSeashells 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.

Natural Curiosities 1


Collection of natural curiosities on my mantlepiece

A collection of natural objects displayed on my mantelpiece at the moment, along with a postcard of a watercolour painting The Pelicans by the artist Angela Gladwell (

Click once on the image to find out what the objects are.

Click twice or three times to see the details of the objects.

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.

Shell Sand on Herm

Image showing size of small seashells in shell sand from Herm in the Channel Islands

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.

Ringstead Bay Fossil Bivalve – Ctenostreon proboscideum

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.


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Wind-sculpted sand & shells at Rhossili

Beach surface textures carved by windblown sand

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.

Beach surface textures carved by windblown sand

Beach surface textures carved by windblown sand

Beach surface textures carved by windblown sand

Beach surface textures carved by windblown sand

Beach surface textures carved by windblown sand

Beach surface textures carved by windblown sand

Beach surface textures carved by windblown sand

Beach surface textures carved by windblown sand

 Revision of a post from 24 December 2009


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Arrangements of Seashells

Arrangement of Seashells 1 - Mostly small variegated scallop shells with a Manila Clam, top shells, and sea glass, in a bowl of water - common British seashells.

I really like to look at shells and have them around me. I often discover the odd shell in my pocket as a souvenir of a trip to the beach. Sometimes I will collect empty shells in larger numbers where this is permitted. The pictures in this post show different assortments and arrangements of common British seashells that have decorated my home from time to time over the last couple of years.

There are many posts on Jessica’s Nature Blog about seashells – sometimes just showing pretty pictures (like here) but often also describing their identifying features and other information. Click here if you would like to browse through more than 60 SEASHELL POSTS.


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Baby barnacles on Rhossili rocks

It’s not just the birds, bees, and educated fleas that do it, the barnacles do it too ….. breed in springtime, that is! The results were there for everyone to see, with millions of miniscule baby barnacles smothering the rocks at Rhossili in Gower in early April.

Each newly settled barnacle measured just a millimetre or so. [It was at the limit of the camera’s capability to focus – so apologies if the images are not as sharp as they could be]. The baby barnacles develop from free-swimming cyprid larvae that are only 500 – 800  µ m long. The cypris is the final stage in the larval development of the acorn barnacle – following six consecutive stages as a nauplius larva.

The cypris looks a bit like a tiny clam or an ostracod with two large shells or valves hinged on the dorsal surface and open on the ventral one. Six pairs of fringed appendages used in swimming hang down from between the valves. The cypris has sense organs to detect suitable surfaces on which to settle. It also has small antennules at the head end which it uses to crawl over the chosen substrate before performing a head-stand and cementing itself into position on its back. Newly settled barnacles are referred to as spat.

The shell of the settled acorn (or sessile) barnacle has six over-lapping calcareous side panels making an approximately cone-shaped wall. The animal lives within this ‘box’. Four more hinged plates create a lid to the box that can be opened and closed. Once the new adult-like shell form is developed, the fringed swimming appendages or natatory cirri of the larva can then be protruded through the hinged lid plates to seive food particles from seawater.

[You can see more detail in the photographs if you click on the images once, or twice. If you look carefully, you should be able to recognise a few cyprid larvae with their smooth, glossy translucent shells, in the process of settling amongst the recently metamorphosed miniature adult forms].

The young barnacles settled on every patch of smooth, bare rock where it was available at the base of Rhossili cliff – but also on top of other living adult barnacles, on the old white calcareous bases left by detatched large Perforatus perforatus barnacles, on limpets, and on mussels.  Only the dog whelks with their variously coloured shells seemed mostly free from spat fall as they feasted on the mussels and barnacles.


Revision of a post previously published 18 May 2010


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Winkles living on Whiteford wood and rocks

Common winkles, Littorina littorea (Linnaeus), grazing on ancient wood at Whiteford Sands, Gower, South Wales, UK (1) 

On the beach at Whiteford, near Llanmadoc in Gower, there is one place where many boulders and occasional water-logged timbers outcrop on the sands. The rocks could well have been deposited by an ice-sheet, while the wood may well be the remains of a forest that was submerged ten thousand years ago.

At low tide, hundreds of thousands of common winkles, Littorina littorea (Linnaeus), emerge from hiding places under stones and sand.  You can see trails in the sand showing how they travel to exposed hard surfaces on rocks and wood to feed. These surfaces may be covered with acorn barnacles but the winkles are vegetarians and are not interested in eating these. The winkles are after the thin encrusting film of microscopic green algae which coats every surface. Winkles have a sort of rough tongue called a toothed radula which they use to scrape this deposit off the surfaces.

Huge numbers of empty winkle shells can occur on the strandline at Whiteford. Many of the empty winkle shells found there, on the sandy spit beyond the point, have started life on the stones and boulders around the old Whiteford lighthouse. 

In common with these drifts of empty winkle shells on the strandline, the shells of these living specimens of gastropod mollusc are also thick and rough with a dull and worn surface. In close-up the shells also appear pitted; pitting can be caused by a lichen living in the matrix of the shell. 

In other locations in Britain – like the seashore along the Jurassic Coast in Dorset – the shells of the living common winkles are not dull and rough like the Whiteford shells: they look very different. You can see some photographs of these, for example, in the post called Holdfast habitat at Ringstead Bay.

Common winkles, Littorina littorea (Linnaeus), grazing on ancient wood at Whiteford Sands, Gower, South Wales, UK (2) 

Here is an ancient piece of wood projecting from the sand. At its base you can see the trails in the sand left by winkles as they move towards this hard surface. The winkles congregate at the base of the timber and climb upwards along the worn grooves to graze the algae.

Winkles on wood at Whiteford Sands: Common winkles, Littorina littorea (Linnaeus), grazing on ancient wood at Whiteford Sands, Gower, South Wales, UK (3)  

Here is a close-up view of the winkles grazing on the eroded surface of a piece of old water-logged wood.

Living winkles on pebbles: Common winkles, Littorina littorea (Linnaeus), grazing on alga-covered pebbles at Whiteford Sands, Gower, South Wales, UK (4)  

A scattering of  living winkles are also found feeding amongst the smaller, smoother, algae-coated stones.

Living winkles on rock: Common winkles, Littorina littorea (Linnaeus), eating algae from boulders on the beach at Whiteford Sands, Gower, South Wales, UK (5)  

On larger boulders the winkles are tightly clustered together and may entirely cover the surfaces. In the picture below you can see how dull and worn the shells are. Some of them have grains of sand sticking to them and a few even have barnacles attached.

Winkles at Whiteford Sands: Common winkles, Littorina littorea (Linnaeus), scraping microscopic algae from boulders on the beach at Whiteford Sands, Gower, South Wales, UK (5)  

Revision of a post first published 24 September 2009


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