The stony west bank of Pennard Pill

Sea Lavender on lichen covered stones of the river bank at Three Cliffs Bay Just before the Pennard Pill watercourse takes a dramatic swing to loop around the giant sand dune to get to the shore at Threecliff (Three Cliffs) Bay on the Gower Peninsula, the right hand or west bank is composed of rough stones and then transitions into a salt marsh. [The area lies on the opposite side of the river to a more substantial and higher shingle bank that can be reached via a set of concrete stepping stones].

The low shingle surface of the right bank is relatively stable. Despite regular tidal inundations of brackish water, life clings to the limestone. Last August it was particularly attractive, covered with bright patches of yellow and black lichens, and ground-hugging clumps of partially red-stemmed plants with clusters of small pink flowers. I will have to find out what these plants are the next time I visit. I didn’t take close-ups. I had thought they might be Sea Heath (Frankenia laevis) but apparently that does not grow in this area – although it likes the same kind of habitat.  I think Sea Sandwort was also present. However, the numerous flowering stems of Sea Lavender I did recognise; and these plants were found equally spread in stony ground and on the wetter salt marsh area.

An Oyster Shell with a Black Pearl

Oyster shell with attached pearl

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.

Tracks and Trails on Whiteford Sands

Furrowed trails made by common winkles on wet beach sand

You don’t exactly have to keep your nose to the ground to see them but you do have to be a keen observer to notice all the different tracks and trails left on the soft wet sediments of the beach at low tide. Larger marks left by people and vehicles are the first ones you see. Bird footprints are every where. The birds are feeding on all sorts of invertebrate seashore creatures like worms, small crustacea and molluscs – all of which leave holes, burrows and furrows as they move in and out of the sand and across the surface. Some of the pictures shown here simply aim to give the general context for the area of Whiteford Sands that I was walking across. If you look closely the other images, you will see not only the ripples in the sand but also the intricate network of traces left by the virtually invisible organisms that inhabit this ecosystem. The larger furrows in photos 1, 12 and 13 are made by the common winkle (Littorina littorea Linnaeus). I cannot name each animal that is responsible for each of the other types of trace. However, I am sure that there will be some specialists out there who could, especially those researchers concerned with the interpretation of trace fossils (the ichnologists).

Click images to view full size.

View looking west towards the sea at Whiteford Sands

View looking north-east towards the dunes at Whiteford Point

Wet seashore sand with marine invertebrate and other tracks and traces

Wet seashore sand with marine invertebrate tracks and traces with bird footprints

View looking north-east over wet seashore sand ripples with marine invertebrate tracks and traces at Whiteford Sands

Wet seashore sand ripples with marine invertebrate tracks and traces

Wet seashore sand ripples with marine invertebrate tracks and traces

Wet seashore sand ripples with marine invertebrate tracks and traces

Wet seashore sand ripples with marine invertebrate tracks and traces

Wet seashore sand ripples with marine invertebrate tracks and traces

Furrowed trails made by common winkles on wet beach sand

Furrowed trails made by common winkles on wet beach sand

River Cerne near Charminster

Water-logged sheep pasture by the River Cerne

The heavy rains of the past few weeks have stopped for the moment but the River Cerne is still swollen and the water table raised so that fields are boggy and covered with pools. The stretch of this small chalk river between the villages of Charlton Down and Charminster in Dorset, England, is shown in the images here. Most of the shots are taken from the east side of the valley following the Cerne Valley Trail (14 January 2016). At one point the engorged river channels itself under a narrow footbridge of re-used railway sleepers and gushes out downstream with waves and foam. In another place, a bank-side tree has lost the footing for its roots and leans right over the water. Ripple-strewn and reflecting shallow ponds have accumulated in the sheep pastures, while the area by the ford has over spilled into Mill Lane making it look like a canal and tow path.

The tree-lined winding course of the River Cerne north of Charminster

Large shallow lake of flood water in sheep pasture near Charminster

The flooded road at Mill Lane near Charminster

Flooded lane near the ford in north Charminster

River swollen to the top of the banks near Charminster

A small tree leans precariously over the swollen River Cerne

The swollen river water gushes out downstream of a footbridge

Flooding around a foot bridge over the River Cerne

Bankside trees reflected in flood waters in sheep pasture

Traces on the shore at Whiteford (1)

Sandgrain tubes of marine worms and sea shells

Fossils can include not only the actual preserved remnants of organisms from times long past (like shells and bones), and the replacements of such organisms (such as infilled moulds and casts), but also the evidence of their existence – for example their modified habitats, trails, burrows, tubes, marks and structures left by their feeding activities. Such evidence of long dead creatures is referred to as trace fossilisation; and the study of fossil traces is termed ichnology.

Part of the process of identifying the exact nature of trace fossils and reaching an understanding of their significance, involves making observations of the behaviour of related or similar present day organisms. This includes a study of their activities and the impact of them on their immediate environment in life. It also involves making records of the way in which the organisms change – what happens to them and their habitat after death (taphonomy).

Many of the trace fossils which I have discovered while walking along seashores and looking at cliffs, outcrops and boulders on beaches were made by various invertebrate seashore creatures in soft intertidal sediments that have later been buried, compressed, and hardened into rock. Recent marine worm tubes of various kinds are a fairly common occurrence on beaches and also as fossils in the sedimentary rocks of, for example, the Dorset coast in England. A short while ago I posted some photographs of fossil worm tubes that I found at Winspit.

For these reasons I was particularly interested to see the millions of sand grain tubes of marine polychaete worms on the low tide beach at Whiteford Sands on the north coast of the Gower Peninsula in South Wales. Many could be seen in situ, no doubt with worms in residence, projecting from the surface of the wet sand like some kind of stunted crop with seashells scattered among them. On the shallow bank created by a beach stream wending its way seawards, it was fascinating to see how far down into the sediments the tubes extended, a thick layer of unknown depth. It reminded me of a fantastic illustration in a book I recently acquired by Wilhelm Schäfer called Ecology and Palaeoecology of Marine Environments, originally published in Edinburgh by Oliver & Boyd in 1972. Copyright considerations mean the book is not old enough for me to reproduce the drawing here for you without written permission but Figure 190 on page 326 shows a cross-section through bedded sands and muds and shell deposits with many-branched and frequently extended dwelling tubes of Lanice conchilega cutting across the layers – just like the deposits on Whiteford Sands. Even though the book is old it is still widely available secondhand and is a wonderful repository of information.

Seaweed at Rocquaine Bay

Seaweeds growing on a mooring rope at low tide

Sand-filled embayments occur among the rocky outcrops on the wide sweep of Rocquaine Bay. This bay is on the west coast of the Channel Island of Guernsey. The embayments are strewn with mooring chains, ropes and buoys that provide good anchorage points for small fishing boats, leisure craft and seaweed.

Velvet Horn Weed (Codium fragile) was growing profusely on one particular mooring rope this autumn. It was also living in rock pools further north on the shore. I was surprised to see it in such abundance because it seems to be one of the less common marine algae on the Dorset coast where I had seen it only a couple of times before. Its dark green branched fronds have an unusual spongy texture due to a thick covering of fine “hairs”. The Velvet Horn dominated for many metres along the rope towards the blue buoy but elsewhere it combined with a wide variety of seaweeds such as Irish Moss (Chondrus crispus), Toothed Wrack (Fucus serratus), and an assortment of filamentous red and green algae to cling in decorative clusters on the rope.

Seaweeds growing on a mooring rope at low tide

Seaweeds growing on a mooring rope at low tide

Seaweeds growing on a mooring rope at low tide

Seaweeds growing on a mooring rope at low tide

Seaweeds growing on a mooring rope at low tide

Seaweeds growing on a mooring rope at low tide

Shallow Rock Pools at Winspit

Seashore life in shallow rock pools on a limestone ledge

The flat quarried limestone ledge on the water’s edge at Winspit in Dorset provides a slightly unusual substrate for seashore life. There are natural gullies and deep angular man-made inlets in the stone but the area is mostly characterised by an extensive network of very shallow rock pools. Although only capable of retaining a centimetre or two of salt water as the tide recedes, these shallow pans and the surrounding surfaces are intensely colonised by numerous marine organisms, The natural patchwork of seaweeds and seashore creatures resembles a vast multi-coloured carpet with predominating pink and green hues.

The depressions in the rock are caused by the differential erosion of the softer limestone and the more resistant black chert nodules liberally embedded in it. The chert is composed of hard quartz derived from the opaline silica of decomposing sea sponges millions of years ago. The exposed rock stratum belongs to the Portland Chert Member dating from the Jurassic Period. Physical wear and acid erosion affect the softer matrix by chipping away and dissolving the stone respectively. The result of these ongoing processes can be seen from the small pitting marks.

In addition to this, the colonising organisms contribute significantly to erosion processes. For example, encrusting lichens can penetrate the rock surface, and as limpets feed by scraping this and other types of biofilm from the surface, they incidentally remove minute particles of stone with the food. Over great periods of time this feeding behaviour, together with other natural phenomena, imperceptibly degrades and removes rock thereby increasing the depth of the depressions. Additionally, the limpets always return to a home base when the tide goes out, and the circular impressions left by the friction of the shell margin as the limpet suckers tight down to prevent moisture loss are evident everywhere. When a large limpet dies or is removed, the home base is frequently re-occupied by new generation small limpets.

The natural depressions retain water at low tide, sometimes just a few millimetres but enough to support continued activity and prevent dessication. The wet hollows and much of the surrounding rock are covered by a patchwork of black, green, pink and white encrusting lichens and algae with groups of sessile or acorn barnacles. Some of the encrusting algae are calcareous, and there are abundant short tufts of pink calcareous coral weed, branched and articulated. Soft, finely-branched and filamentous red algae also occur – sometimes  amusingly attaching themselves like decorative plumes to the shells of living limpets which often provide a home for dark brown encrusting algae, while dark red, almost black, beadlet anemones also glisten in the water.