A wide and shallow river flows over the sandy beach at Ventry Bay on the Dingle Peninsula in Ireland. I do not know its name. Characteristic ripple marks are made in the wet sand around the margins of its wandering channels, showing the influence of the freshwater currents modified by the sea water tides. As you walk away from the fast flowing water, the overlapping ‘leaf’ patterns made by the river currents gradually transition into the parallel ridges of wave-induced ripples that are more typical of the intertidal shore .
Images of patterns on the beach caused by wave action winnowing out lighter black sediments from the heavier yellow sand grains have been shown in earlier posts. Here are three microphotographs of the black sediments from a small sample that I scooped up on the shore at the time. Sorry there is no scale because I haven’t fathomed out how to include one in the images yet.
Hopefully these shots are clear enough to show that the numerous black particles are small fragments of waterlogged wood; shiny hard pieces of coal (coal dust); a few large pale seeds not yet identified; minute fragmented seashells such as mussels; and many white slender organic objects which I think are small fish rib bones but could be or include heart urchin spines. It was these bones that gave the dried sample in the petri dish an almost fibrous appearance. I am going to see if I can find someone from the world of archaeology who would be familiar with the analysis of this type of material – to see if I can get some more specific information about these black sediments from the beach at Rhossili in Gower.
Patterned Sand 8 – 14: Naturally formed patterns of black sediment on yellow sand were photographed on the beach at Rhossili Bay, Gower, in April 2017. The black sediments were mainly composed of minute pieces of rotten wood, coal dust, and miniscule fish bones, with a small proportion of seeds. The images have been digitally colour-enhanced to emphasise the patterns of this natural abstract art.
Patterned Sand 1-7 – Naturally formed patterns of black sediment on yellow sand were photographed on the beach at Rhossili Bay, Gower, in April 2017. The black sediments were mainly composed of minute pieces of rotten wood, coal dust, and miniscule fish bones, with a small proportion of seeds. The images have been digitally colour-enhanced to emphasise the patterns of this wonderful natural abstract art.
Nearing the end of my walk now from Hill End to Spaniard Rocks and back again. The damp sand for hours exposed to air revealed in the oblique light intricate traceries of trails where small invertebrates had travelled around unseen on the surface to hunt for food. The tide had turned and was fast washing the shore clean again. First the light particles of wood and coal dust floated away and gradually all the other organic debris and flotsam were removed in order of weight. Just a few items left to go. Incredibly, a soggy soft pink toy starfish found itself marooned with a real starfish. I photographed it exactly as I found it. The red mooring buoy seen high and dry earlier in the day was now licked by the waves, along with paired prickly cockle shells, living whelks, a dead dogfish, and a wellington boot.
The sun was bright and the sea was dark blue and scintillating. Rows of sand ripples reflected the blue sky like a natural abstract painting. Such a view of the sea and sand in Rhossili Bay is one of the most uplifting I know.
I reluctantly left the water’s edge to negotiate the makeshift bridge across Diles Lake once more. This time I photographed the unattractive brown periphyton attached to the underwater rocks as well as the beautiful sunlit surface ripple patterns of the flow. While it was time for me to leave, others were just arriving with surf boards, impatient to immerse in the iridescent sea – now that must be some high on such an afternoon. I can’t wait to go back.
As my walk continued from Hill End northwards on Rhossili beach, the dark drift patterns and fine strandline debris covering the sand eventually faded away to be replaced by dry sand ripple and swash/backwash patterns before arriving at the extreme north-east corner of Rhossili beach. This is the place where much of the flotsam ends up. It is not that Gower visitors are careless with their trash. Most of this stuff comes from far afield – sometimes as far away as South America. It does get periodically cleared away but is difficult to manage because the rubbish arrives and leaves with each tide, and can get buried or revealed from one high water to the next. Bicycle wheels, brightly coloured plastic pieces, fishing net and ropes, toothbrushes, balloon stoppers, and flip flops are common items along with the driftwood. The pile of organic and plastic rubbish lies adjacent to Spaniard Rocks which connect the tidal island of Burry Holms to Llangennith Burrows.
The geology here is interesting but on this occasion I focussed on the seaweeds which attach to the rocks along the water-filled channel between Burry Holm and Spaniard Rocks. There are many types intermingled. They include amongst others the brown Fucoid algae such as Toothed Wrack (Fucus serratus) , Spiral or Flat Wrack (Fucus spiralis), and Egg or Knotted Wrack (Ascophyllum nodosum). Bladder Wrack or Pop Weed (Fucus vesiculosus) was also present but not in its typical form. The numerous small, paired, almost spherical air bladders typical of the species were few and far between on specimens in the area where I was looking – so that there is confusion in my mind as to the identity of some of the weed I have named as Spiral Wrack.
There were also some red algae of the thin bladed type that dry out between tides into blackened streaks on the rocks (of the kind to which the lavabread seaweed belongs). Another red alga was the Sand Binder seaweed (Rhodothamniella floridula) which forms small humps of fine filaments trapping sand grains on rocks low on the shore; it is often found beneath the taller stalked fucoids. Finely branching red Polysiphonia lanosa was epiphytically attached to the Egg Wrack.
Of special interest this visit was the fact that the seaweeds were getting ready to reproduce. The Spiral Wrack had swollen receptacles on the forked frond tips that were not fully ripened yet. However, the Egg Wrack was ready to go. It has separate males and females. The male receptacles are bright golden green studded with orange pustules (conceptacles) that release a colourful fluid containing the sperms. I had seen these and reported on them before. This time I also saw the female receptacles which were dull green and covered with minute darker almost black blisters (conceptacles) containing the eggs. It almost seems as if you can see the eggs when you zoom in on the picture – actually just the light bouncing off the ripe eggs within the pustule.
The next stage of the walk from Hill End to Spaniard rocks saw an even greater reduction in the numbers of washed up starfish, and correspondingly greater concentrations of seashells in the strandlines, mostly empty shells of the bivalve Pharus legumen. The fine black detritus arranged itself in elaborate patterns mostly to do with the drainage of water back down the beach.
The sample of the fine dark particles that I took at the time, turns out to have a very interesting composition now I have had a chance to examine it under magnification back home. There is a fair proportion of small dark decaying wood fragments but most of the black material is composed of minute shiny hard particles of coal (what you might call coal dust). The coal is not difficult to account for since coal mining and its export from nearby docks was a major industry in the past. There are many ways the coal could have been accidentally deposited in the sea. Together with the coal dust there are various seeds that I am not able to identify and, most surprisingly of all, what seem to be myriads of delicate fish bones. In fact, so many small threadlike rib bones that the dried sample seemed to have a fibrous texture. Amazing.
As I walked further along the beach from Hill End to Spaniard Rocks, I realised that there were maybe four or five strandlines lying parallel to each other and to the water line. Each line of mainly organic debris was slightly different in its constituents. Similarly, there were changes in the make up and proportions of the animal and plant debris in the strandlines in a linear way as I walked from south to north along the shore. The starfish became less numerous and the numbers of bivalve molluscs and their shells increased,
Most noticeable was the way in which the darker particle component of the strandlines became separated out on the up-shore side of the lines, and formed patterns contrasting with the yellow sand on which it lay. Sometimes there were branching lines of clear spaces, like rivulets running through the black stuff. Sometimes, the black pieces followed and echoed the shallow ripple marks in the sand – either as parallel lines or cross-hatching designs full of beautiful natural abstract compositions. In other places, small obstacles such as seashells had formed little dams to impede the flow of lighter, darker, material as the water that carried it swashed and backwashed over the beach, and this had created distinctive patterns as the water flowed around the barriers.
I was curious about what made up the fine black material responsible for the patterns. I took some samples to look at under the microscope when I got home.
The sky became bluer and the vast expanse of low tide sand seemed superficially at least to be featureless – but peering into the distance, towards Burry Holms, there was an unexpected dark line. Viewed through the zoom, it turned out to be something interesting on which dozens of young gulls and a few crows were having a great feast.
During the early hours of the morning the sea had brought in a sad harvest of seashore creatures now lying dead or dying on a bed of broken plant stems and fragments of blackened driftwood. Most of the animals were common starfishes (Asterias rubens) but rayed trough shells (Mactra stultorum), the elongated Pharus legumen, common whelks (Buccinum undatum), and the occasional masked crab (Corystes cassivelaunus) were also present. What had caused this mass stranding event I do not know but it happens every now and again. I have photographed similar multiple deaths on this beach before.
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Diles Lake is really a stream that drains the Llangennith marshes lying behind the dunes at Rhossili in Gower. The water is frequently dammed back to resemble a lake by banks of pebbles pushed upshore by strong tides – but the water always works its way through the pebbles and sand to flow across the beach, spreading out into myriads of shallow channels as it approaches the sea. Underwater, the many colours of the pebbles are clear to see, contrasting with the dry stones stacked to the side often showing a black coating caused by earlier burial at deeper anaerobic levels of the beach.
It can be quite tricky to cross the stream but on this occasion someone had conveniently made ‘stepping stones’ from an old pallet and driftwood. I noticed that the stream exiting the dunes had long trailing clumps of unpleasant-looking brown filamentous algae of a type resembling something more typical of polluted water – but I must have been mistaken because the water sampling point for Rhossili is nearby and it has only recently been declared of excellent bathing quality.
The heaped pebbles once over the stream had brightly coloured pieces of knotted rope from fishing activities and a scrunched up newspaper (perhaps it had held bait). My eye was also caught almost immediately by a much larger piece of vivid flotsam washed up and stranded at mid shore level. It was about 1 metre in diameter and hip high and made quite a sculptural addition to the beachscape. Faint embossed lettering provided the clue I needed to do an internet search and discover it was a wrecked rigid mooring buoy style MB350 made by the Norfloat company in Exeter.
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