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.
Some still-life studies of white or cream-coloured natural objects on a black background: showing rounded white chalk pebbles from the Dorset coast in England; ribbed cockle-like bivalved seashells from Queensland in Australia; and a piece of bleached white coral skeleton washed ashore from the Great Barrier Reef.
The wide sandy beach at Ventry lies on the south coast of the Dingle Peninsula in Ireland and is home to a small harbour where boats leave for tours of the Blasket Islands, and it also marks the route of an ancient pilgrims’ way. According to the sign posted in the car park, the Saints’ Road (Cosán na Naomh) starts here in Ventry (Tráigh Fionnetrá) and finishes in Baile Breac at the foot of Mount Brandon over 18 km away. It is today waymarked by the symbol of a monk, and is thought to have been in existence for over a thousand years.
The notice says that “In Old Irish literature, this beach was the scene of a somewhat mythical encounter known as Cath Fionntrá (the battle of Ventry) in which the great hero Fionn Mac Cumhaill overcame the Emperor of all the World except Ireland, Daire Donn”. Now all is calm on the beach with the only sign of struggle being that of the sea against the land. The sand is strewn with pebbles, shells, and sea weed; while the dunes are protected from erosion as in so many other places these days by the placement of large boulders (a structure known as rip-rap).
Just a few pictures from my visit to Ventry Beach on the Dingle Peninsula on the west Coast of Ireland yesterday selected from the 480 photographs I took! The weather was amazing for September and I was able to spend five hours on the sand enjoying the sights and sounds as well as the atmosphere of this old pilgrims’ path.
Don’t forget, you can click on any photograph to enlarge the image!
This empty Common Whelk shell, picked up on the beach, is mostly covered with the calcareous tubes of a marine polychaete worm called Pomatoceros triqueter, also known as “German writing”. The tubes are a frequent sight on rocks at the beach and also on objects such as pebbles and driftwood. The tubes attached to the outer surface of the shell may have been made while the whelk was still alive and moving about. Those within the mouth of the empty shell were definitely attached after the gastropod mollusc had died and its flesh had been removed from the shell.
Organisms that live on the outside of other creatures in this way are known as epibionts. Usually epibionts are neither parasites that occupy a rather one-sided relationship with the host where they rely on it for nutrients and frequently damage it; nor symbionts where both organisms depend on each other in a mutually beneficial relationship; but maybe they could be called commensals in that the host is not damaged by the attached organism but merely provides a surface of attachment, and both organisms share the same environment.
The images below show the distinct patterns where calcareous tubes of Pomatoceros triqueter have been attached (but now removed) on a pebble at Chesil Cove in Dorset; also some in situ shots of Pomatoceros tubes attached to low shore rocks, along with the sand-grain tubes of the Honeycomb Worm (Sabellaria alveolata), at Mewslade Bay in Gower.
Whelk shell with an encrustation of mostly acorn barnacles – some complete with all plates and in other areas only the basal plate remains
Acorn Barnacles (Cirripedia) settle on almost anything in the sea or on the seashore. These images show the empty shell of a Common Whelk (Buccinum undatum) that I picked up on the beach at Rhossili on the Gower Peninsula in South Wales – it has proved to be an ideal substrate for them.
The outer surface of the shell is almost entirely covered with barnacles. The majority are intact with the lateral and also the terminal plates. Many specimens are mature but there are juveniles too. In one area, the barnacles have been knocked off but you can still see the basal plates by which they were attached. Some barnacles may have been living on this common British seashell while it was still alive. However, it is equally possible that the shell became colonised by barnacles once it was empty. The few calcareous tubes of marine worms which are stuck on the inner surface of the aperture or mouth of the shell would have settled there once the whelk flesh had disappeared.
The close-up shots reveal the details of the structure of the barnacles, made up generally from six fixed lateral plates overlapping each other to form the shell for the animal, with four articulating terminal plates forming the lid to the chamber. The whole barnacle shell is in this instance securely attached to the whelk shell by a basal plate that often remains in place even when the barnacle becomes detached. Not all species of barnacle have a basal plate.
The macro-photographs also show the intricate pattern and texture of the whelk shell surface with a regular criss-crossing of ridges. This gives an almost lattice-like effect where the growth lines intersect with the natural ornamentation or sculpturing of the shell. In close-up, it is also possible to see small areas of the colonial microscopic animals called Bryozoa or Sea Mats (resembling fragments of lace) which are clinging to the bases of some of the barnacle shells.
Close-up image of pattern and texture in a barnacle-encrusted whelk shell
Whelk shell with mature and juvenile barnacles attached
Close-up image of growth lines and natural sculpturing in a barnacle-encrusted whelk shell
Whelk shell with barnacles attached to the outside and calcareous tubes inside