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.
You can click on any picture to see the whole gallery in enlarged format
As the tide ebbed at Rhossili beach one day in November, it left acres of natural patterns in the sand where the receding waves had sifted the grains of different weight and colour, and rearranged them into drunken stripes and zigzags.
This sea shell has a secret. It is the new home of a Hermit Crab, Pagurus bernhardus (Linnaeus). He is very shy. I had to wait very patiently for him to come out of his shell – and then he nearly ran into the lens of the camera!
Revision of a post first published 13 September 2009
From a distance, from a very long way off, it might have been possible to mistake this piece of unusual flotsam for one of the many blue jellyfish that drift ashore at Rhossil Bay in Gower. Actually, just an inflated blue rubber glove – don’t ask me what it was doing there. Some of the things you find as flotsam on British beaches are intriguing.
This picture shows what the real blue jellyfish looks like. You can see why someone might have thought the glove was one. Only this animal is very much bigger than the flotsam. The diameter of the dome can measure upto 90 cm across. This is the Dustbin-lid Jellyfish, Rhizostoma octopus (Linnaeus), also apparently called a Barrel or Root-mouthed Jellyfish.
The colour of these jellyfish is variable. You can compare this specimen from Rhossili – with the top of the blue dome being uppermost and the oral arms just protruding from the dome or bell – with the specimen featured earlier in Monster jellyfish stranded on Whiteford Sandswhich was stretched out with the underside (sub-umbrella or oral surface) and oral arms entirely visible. There’s also more information and pictures in the post Pink Dustbin-lid Jellyfish at Rhossili.
The picture below shows one of a yet another colour variation drifting ashore in shallow water with the incoming tide at Rhossili. Unlike many jellyfish, this type does not have a ring of dangerous stinging tentacles around the outer edge of the large dome or umbrella. However, the upper surface of the umbrella (known as the ex-umbrella or aboral surface) is covered with groups of tiny nematocysts or stinging cells that give a slightly matt appearance to the surface when it is out of water.
More patterns in the sand from Rhossili beach in Gower. Ridges and ripples sculpted by wave action, now revealed at low tide in their wider scale patterns, and showing gradations of colour as the sandy sediments are dried by the wind.
Bright green worms on mussel beds? I have never even noticed them before but I guess they are common from the numbers I found and by accounts I have now read in text books. This is the Green Leaf Worm, Eulalia viridis (Linnaeus). It was photographed writhing around with many others on the mussels and barnacles that were encrusting the vertical faces at the base of the Carboniferous limestone cliffs on the north side of Spaniard Rocks at Rhossili Bay, Gower.
The Green Leaf Worm is one of thirty species of marine polychaete worm belonging to the Family Phyllodocidae in Britain. Although not visible in the photograph above, the worm has a row of paddle-like appendages along each side of its body. These are very lively carnivorous worms that secrete loads of mucus which, no doubt, helps them to wriggle around the rocks at low tide looking for food.
The bright orange patch in the photograph above is encrusting sponge. The light green colour on the rock and the barnacles is a coating of microscopic surface algae. The deep pink tufts are red algae. There was a lot of this seaweed attached to the rocks here, often in a distinct band.
You can see from the pictures below how there is rocky shore zonation of the organisms colonising the limestone surface on Spaniard Rocks.
The deep red stems of Sea Spurge on the sand dunes caught my eye this spring. These plants were found at Llangennith Burrows which backs onto the northern end of Rhossili Bay, Gower. It was rather a dull overcast day so it was especially cheering to see these patches of bright colour. Euphorbia paralias Linnaeus must be a very drought resistant plant to survive in this location.
There were small groups of Sea Spurge just putting on a growth spurt with the advent of a little warmer weather and lots of rain. They were mostly established around the edges of the Marram grass which topped the dunes. I saw this plant at the extreme eastern end of Whiteford Sands too.
It will be interesting to see what this plant looks like in a month or so when it is fully grown and in flower – and I visit Gower again.
Surely one of the most beautiful British marine molluscs, the living Necklace or Moon Shell, Polinices catenus (da Costa), is shown here washed up on the sands of Rhossili Bay, Gower, South Wales.
This gastropod is a carnivorous predator that inhabits the lower shore. It often ploughs a furrow in the wet surface sediments at low tide level as it travels around on incoming tides, searching for small bivalved molluscs on which to feed. It drills through the shell of its prey making a neat circular hole through which it can eat the flesh. The hole is almost invariably drilled near the umbo or hinge area of the valve. It particularly likes to eat Thin Tellins (Angulus tenuis), Banded Wedge Shells (Donax vittatus) and young specimens of Striped Venus Shells (Chamelea gallina).
The photograph below shows the other side of the same living Necklace Shell. The brown chitinous operculum (lid) is visible in the shell opening or mouth where the animal has withdrawn into the cavity of the shell and sealed itself safely inside.
This species of gastropod mollusc derives its name from the shape of the egg masses that it lays. These look a bit like a torque type of necklace – a broad open curved band of eggs.