Pebbles at Whiteford (4)

Pebbles, shells, and a feather on the beach near Whiteford Point

A sand bar spreads southeast from Whiteford Point in Gower, South Wales. At low tide in the Burry Estuary, it is part of a very extensive sandy area over which cockle and mussel fisherman can traverse in vehicles from places further along the north Gower coast. The sand depth is variable and mostly envelops a spit of pebbles. Sometimes the pebbles are entirely hidden. Sometimes they are partially exposed. Intermixed with the pebbles are seashells – cockles, mussels, whelks, and oysters are the most commonly occurring. There is a wide range of colours and textures in the pebbles and they are particularly interesting because of the range of rock types they represent.

As you take a 360 degree scan of the horizon from this isolated expanse of sand and pebbles, there is not a single rocky outcrop in sight. So where have these beach stones come from? The collection includes sedimentary rocks from the locally occurring Carboniferous limestone and Devonian sandstones, mudstones, and conglomerates – like the bedrock exposed at Rhossili and at Broughton Bay. It also includes samples from higher up in the Carboniferous strata such as the Millstone Grits, sandstones, and shales, and Coal Measure layers. These strata underlie the Burry Estuary into which this spit extends, east Gower, and the Swansea district and way beyond. There are many rock types with which I am not familiar but I notice that some are metamorphic and igneous in nature. So how have all these rocks ended up on this spit, far from their place of origin?

Part of the answer is undoubtedly the effect of sea drift, currents, and storms carrying weathered and broken stones along the shores of Carmarthen Bay and into the estuary or inlet – but a significant proportion of the stones are thought to have been brought to the area from considerable distances away by glaciation, and deposited by the melting of an ice sheet, possibly in the late Devensian era about 24,000 years ago. Most of these stones lie hidden in a mass beneath the Whiteford Dunes but some are exposed high on the shore at the foot of the dunes, and beneath the disused iron lighthouse on Whiteford Point. Over time the waves have dislodged the often frost-shattered stones from the surface of the deposit, and washed them further along the beach around the Point to form pebble spits and banks, in the process smoothing and rounding them into the pebbles visible today.

Click here for more posts about Whiteford Sands, Whiteford Point, and Whiteford Burrows.

The South-claw Hermit Crab – Diogenes pugilator

I found this tiny hermit crab scrabbling around in the seaweed and seashell debris of a sandy tide pool beneath Rhossili cliffs. I thought at first that it was just a very small, immature, specimen of the common hermit crab (Pagurus bernhardus Linnaeus) but as soon as I picked it up for a closer look I could see that it was something special because it had a large claw (cheliped) on the left instead of the right. There is only one species with this characteristic – the south-claw hermit crab, Diogenes pugilator (Roux). The mature specimens have a greenish carapace no greater than 11 mm in length.

According to Hayward and Ryland (1998) this crab lives in fairly sheltered sandy bottoms from low water spring tide level down to 35 m, on south and west coasts of the British Isles where it is described as common. It also occurs elsewhere from Holland to Angola, Mediterranean, Black Sea, and Red Sea. Mullard (2006) provides more information, saying that D. pugilator is only found in a limited number of places in Britain and Ireland because it is primarily a warm-water species and may be worthy of further study in relation to climate change since there are signs of it extending its range. It was first recorded in Britain “at Worms Head” from specimens provided by L. W. Dillwyn of Sketty Hall in Gower to Spence Bate in 1850 who described it in Annals and Magazine of Natural History.

The crab can quickly bury itself in clean, well-sorted sand on a gently shelving moderately exposed beach facing southwest where conditions are less turbulent than on steeper beaches. This crab has an interesting extra way of gathering food, in addition to scavenging or eating sediment. While mostly buried in the sand, it can sweep its hairy antennae around in an almost circular motion as a net to capture small edible particles from the water.

South-claw Hermit Crab

References

Hayward, P. J. and Ryland, J. S. (eds) 1995 (revised edition 1998) Handbook of the Marine Fauna of North-West Europe, Oxford University Press, New York, pp 434-437, ISBN 0-19-854055-8.

Mullard, J. 2006 Gower, The New Naturalist Library, Collins, London, pp167-168, ISBN0-00-716066-6.

Nitten Field – flowers for insects and birds

For the fourteenth year running, one of the ancient “Vile” fields at the tip of the Gower Peninsula near Middleton in South Wales, has been specially planted with flowers to encourage insects in summer months and to provide a wide variety of seeds for birds in winter. It is a wonderful sight. This year there is a profusion of short yellow corn marigolds beneath tall bearded stalks of hybrid barley.  When the late evening sun slants low over the field, their whiskers glisten in the golden light. Interspersed through the three acre expanse and standing proud are the large heads of dwarf sunflowers just coming into bloom right now. The pale blue linseed has already flowered and their seeds are ripening. The poppies seem once more to be elusive. Around three sides of the field straggley “stand-and-deliver”, a type of perrenial chicory, forms a wide high border. The blooms are nearly finished but the scattered pale blue flowering remnants are lovely with their spectactular deep blue anthers. The central path through the field is bordered by white wild carrot flowers.

This private field is owned by Gordon and Beryl Howe, who have posted signs around it to tell visitors on the nearby public footpaths, who might be intrigued by the unusual and colourful display, all about this conservation project – you can read the poster with all the details yourself in the gallery of images below.

“Blood” oozing from beach at Whiteford

It looked like blood but of course it wasn’t! Red liquid seemed to be oozing from the sand high on the shore towards the north end of Whiteford Sands on the Gower Peninsula in South Wales, approaching Whiteford Point. I have seen the phenomenon before and wrote about a possible explanation in  the post “Rusty pebbles at Whiteford”. Only on that occasion the seepage was more orange in colour and clearly ferruginous in nature. Yesterday, the liquid seemed much more concentrated and red, like blood, quite spectacular, but perhaps just a trick of the light. These photographs are as taken and not edited in any way as I am uploading them direct from my i-pad. I believe that the iron responsible for colouring the water draining down the shore is derived from an iron pan caused by decomposition of an ancient peat bed beneath the sand. It is possible to see the layers of peat and clay where they are exposed just below the seepage rivulets. The peat and clay layers are increasingly interesting as more logs and stumps of preserved trees and bushes are weathering out. More about these features in later posts.

Rock Textures at Fall Bay (1)

Limestone rock texture on the coast

The rocks at Fall Bay are arrayed like the riffled pages of a book. Layer after layer of Carboniferous Limestone is sequentially spread out across the west side of the bay. Each layer has an observably different texture; some are bioturbated with bioclasts and fossils such as fragmentary crinoids and corals. The bedding planes of some strata have deeply sculptured surfaces from weathering and bioerosion. Lichens, barnacles and limpets colonise the rocks and take advantage of the meagre shelter offered by cracks, crevices, and solution hollows.

Peering into Pools on the Causeway

Common colourful British seaweeds in a rock pool on the Worms Head Causeway

Peering into the rock pools on the Worms Head Causeway in Gower reveals colourful kaleidoscopic patterns of common British seaweeds beneath the rippled clear water.

Rock pool on the Worms Head Causeway in Gower, South Wales

Common British seaweeds in a rock pool

Common British seaweeds in a rock pool

Common British seaweeds in a rock pool

Common British seaweeds in a rock pool

Common British seaweeds in a rock pool

Common British seaweeds in a rock pool

Common British seaweeds in a rock pool

Common British seaweeds in a rock pool

Common British seaweeds in a rock pool

Common British seaweeds in a rock pool

Common British seaweeds in a rock pool

Common British seaweeds in a rock pool

Common British seaweeds in a rock pool

Common British seaweeds in a rock pool

Common British seaweeds in a rock pool

The Seasearch Guide to Seaweeds of Britain and Ireland produced by Francis StP. D. Bunker, Christine A. Maggs, Juliet A. Bridie, and Anne R. Bunker, published by the Marine Conservation Society in 2010, ISBN 978-0-948150-51-7, is a really good book jam-packed with wonderful photographs and clear descriptions of seaweeds to aid identifications.

Patterns in Rhossili Sand, March 2015 (3)

Silvery sand patterns at Rhossili Bay

One rainy morning I walked the coastal path along the terrace at the foot of Rhossili Down in Gower. Clouds shrouded the slopes of the Down above me. Ahead of me, Burry Holms and Llangennith Burrows were part concealed by mist. Below me, the tide was going out – far out. The sand on the beach was still wet from the waves and the rain. Slowly the cloud cover thinned and allowed a filtered light to penetrate. The pale light was reflected by the shore, high-lighting the sea-sculpted rows of ridges and ripples in gentle gleaming silver. A stream cascading from the height of the Down worked its way down to the beach, where it spread out in a fan of interweaving channels that cut across the parallel ridges on its way to the water’s edge. Coloured sediments carried by the stream tinted the silvery patterns and made them seem opalescent.

Silvery sand patterns at Rhossili Bay

Silvery sand patterns at Rhossili Bay

Silvery sand patterns at Rhossili Bay

Silvery sand patterns at Rhossili Bay

Silvery sand patterns at Rhossili Bay

Silvery sand patterns at Rhossili Bay