Baby barnacles on Rhossili rocks

It’s not just the birds, bees, and educated fleas that do it, the barnacles do it too ….. breed in springtime, that is! The results were there for everyone to see, with millions of miniscule baby barnacles smothering the rocks at Rhossili in Gower in early April.

Each newly settled barnacle measured just a millimetre or so. [It was at the limit of the camera’s capability to focus – so apologies if the images are not as sharp as they could be]. The baby barnacles develop from free-swimming cyprid larvae that are only 500 – 800  µ m long. The cypris is the final stage in the larval development of the acorn barnacle – following six consecutive stages as a nauplius larva.

The cypris looks a bit like a tiny clam or an ostracod with two large shells or valves hinged on the dorsal surface and open on the ventral one. Six pairs of fringed appendages used in swimming hang down from between the valves. The cypris has sense organs to detect suitable surfaces on which to settle. It also has small antennules at the head end which it uses to crawl over the chosen substrate before performing a head-stand and cementing itself into position on its back. Newly settled barnacles are referred to as spat.

The shell of the settled acorn (or sessile) barnacle has six over-lapping calcareous side panels making an approximately cone-shaped wall. The animal lives within this ‘box’. Four more hinged plates create a lid to the box that can be opened and closed. Once the new adult-like shell form is developed, the fringed swimming appendages or natatory cirri of the larva can then be protruded through the hinged lid plates to seive food particles from seawater.

[You can see more detail in the photographs if you click on the images once, or twice. If you look carefully, you should be able to recognise a few cyprid larvae with their smooth, glossy translucent shells, in the process of settling amongst the recently metamorphosed miniature adult forms].

The young barnacles settled on every patch of smooth, bare rock where it was available at the base of Rhossili cliff – but also on top of other living adult barnacles, on the old white calcareous bases left by detatched large Perforatus perforatus barnacles, on limpets, and on mussels.  Only the dog whelks with their variously coloured shells seemed mostly free from spat fall as they feasted on the mussels and barnacles.

 

Revision of a post previously published 18 May 2010

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Lugworm casts at Whiteford Sands again

Lugworm cast on beach: Close-up of the natural pattern of sandy coils in a lugworm cast on the beach at Whiteford, Gower, South Wales (1) 

I couldn’t resist taking photographs of the lug worm casts on Whiteford Sands again. There seemed to be more than ever in October. I was struck by the patterns they made. First of all, the patterns within the worm casts themselves – the shape similar to the one you’d get if you had squeezed out the entire contents of a tooth paste tube in one spot – only made of sand. An incredibly long and sinuous unbroken sandy coil. These casts were huge.

The second type of  pattern was made by the arrangement of the thousands and thousands of casts and burrow holes on the sea shore – especially where it was covered by a gleaming surface layer of seawater that reflected not only the blue of the sky but the image of the worm casts as well – this made the mounds of sand look twice the size from a distance.

The worm cast patterns could perhaps be considered as naturally-occurring abstract designs. I played around with computer-generated effects to see how they would look. Applying the high solarization effect results in a scene that looks almost moonlit, or a negative image, and for full impact is perhaps best seen with the photograph blown up to highest extent.

The casts were really big. I don’t know whether this was because the worms were taking advantage of sediments that were particularly enriched with microscopic nutrients. Or whether it was the opposite scenario, where a vast quantity of sand had to be quickly passed through the gut of the worm in order to extract the meagre distribution of food particles.

Whatever the case, I don’t think I have seen so many casts at this location midway along the beach before. Mostly I have seen them much further eastwards beyond Whiteford Point. I may be wrong, but I think I remember hearing that the water in the Loughor estuary has become enriched by stormwater and sewage overflow in recent years and this has been suggested as a possible indirect cause for the mass deaths in the cockle populations in the area. I wonder if this is connected to the the apparent population boom in lug worms?  

There is more about these marine worms in the earlier post Lug Worms at Whiteford Sands.

Lugworm casts on the beach: View looking north north-east along the beach showing lugworm casts at Whiteford Sands, Gower, South Wales (2)

Lugworm casts at low tide: View looking west across the Loughor estuary showing intertidal lugworm casts at Whiteford Sands, Gower, South Wales (3) 

Lugworm casts at Whitefprd Sands: Natural pattern of lugworm casts and burrows in damp sediments on the seashore at Whiteford Sands, Gower, South Wales (4) 

Patterns in nature: Natural abstract pattern of lugworm casts on wet sand at Whiteford Sands, Gower, South Wales (5) 

Pattern of lugworm casts: Digitally manipulated image of natural abstract pattern of lugworm casts on wet sand at Whiteford Sands, Gower, South Wales (6) 

Natural abstract pattern of lugworm casts on wet sand at Whiteford Sands, Gower, South Wales (7) 

Pattern in nature: Digitally manipulated image of natural abstract pattern of lugworm casts on wet sand at Whiteford Sands, Gower, South Wales (8) 

Natural abstract pattern of lugworm casts on wet sand at Whiteford Sands, Gower, South Wales (9) 

Patterns in nature: Digitally manipulated image of natural abstract pattern of lugworm casts on wet sand at Whiteford Sands, Gower, South Wales (10) 

Revision of a post first published 2 December 2009

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Necklace Shells & their eggs at Rhossili Bay

Living Necklace or Moon Shell, Polinices catenus (da Costa), on the sandy shore of Rhossili Bay, Gower, South Wales (1)

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.

Living Necklace or Moon Shell, Polinices catenus (da Costa), showing operculum, washed up on the sand at Rhossili Bay, Gower, South Wales (2) 

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.

The egg mass of the Necklace or Moon Shell, Polinices catenus (da Costa), on the sand of Rhossili Bay, Gower, South Wales (3)

Revision of a post first published 15 May 2011

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Mussel shells in the wet sand

Empty common mussel shell (Mytilus edulis L.) on the rain-pitted wet sand of Whiteford Beach, Gower, West Glamorgan, UK (1) 

Thousands upon thousands of paired edible mussel shells lay semi-embedded in wet, rain-pitted sand at Whiteford in Gower. These shells often wash ashore and accumulate in dry piles along the strandlines from the natural mussel beds just offshore. On this occasion, unusually, the shells were trapped and scattered widely across the shore like so many petrifying blue butterflies stranded in the sediments.

Two empty common mussel shells (Mytilus edulis L.) on the rain-pitted wet sand of Whiteford Beach, Gower, West Glamorgan, UK (2) 

Empty mussels shells (Mytilus edulis L.) in the rain-pitted wet sand at Whiteford, Gower, West Glamorgan, UK (3) 

Two empty mussels shells (Mytilus edulis L.) in the rain-pitted wet sand at Whiteford, Gower, West Glamorgan, UK (4)

Empty mussels shells (Mytilus edulis L.) semi-embedded in the rain-pitted wet sand at Whiteford, Gower, West Glamorgan, UK (5) 

Empty mussel shell (Mytilus edulis L.) in the rain-pitted wet sand at Whiteford, Gower, West Glamorgan, UK (6) 

Empty mussel shells (Mytilus edulis L.) in the rain-pitted wet sand at Whiteford, Gower, West Glamorgan, UK (7) 

Empty mussel shells (Mytilus edulis L.) with a footprint in the rain-pitted wet sand at Whiteford, Gower, West Glamorgan, UK (8) 

Some of the many thousands of empty mussel shells (Mytilus edulis L.) scattered across the beach in the rain-pitted wet sand at Whiteford, Gower, West Glamorgan, UK (9) 

Revision of a post first published 4 May 2010

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Birch bark patterns on beach driftwood

Birch bark abstract pattern on driftwood from the strandline at Whiteford Sands, Gower, West Glamorgan, UK, (1) 

Interesting abstract and repeating patterns, smooth and rough textures, light and dark colours: aspects of the contrasting and naturally occurring designs on the bark of a piece of birch tree driftwood, found on the strandline at Whiteford Sands, Gower.

Coarse, dark, reticulated Birch bark pattern on driftwood from the strandline at Whiteford Sands, Gower, West Glamorgan, UK, (2) 

Contrasting light and dark colours, smooth and rough textures, and abstract versus reticulated pattern on a piece of Birch tree bark on driftwood at Whateford Sands, Gower, West Glamorgan, UK (3)

Natural rough dark pattern around a knot in Birch tree bark on driftwood at Whiteford Sands, Gower, West Glamorgan, UK (4) 

Natural rough dark reticulated bark pattern of Birch driftwood against wet sand at Whiteford , Gower, West Glamorgan, UK (5) 

Rough reticulated pattern in Birch bark on driftwood found atWhiteford beach, Gower, West Glamorgan, UK (6) 

Silver Birch driftwood on the strandline at Whiteford Sands, Gower, West Glamorgan, UK (7)

Silver Birch bark pattern and texture on driftwood from the strandline at Whiteford Sands, Gower, West Glamorgan, UK (8) 

Revision of a post first published 5 May 2010

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Turban Top seashells from Weymouth

An assortment of Turban Top Shells washed out by winter waves from rotted seaweed lying buried under sand at Weymouth, Dorset, UK - part of the Jurassic Coast (1)

I love the colours, patterns and sculpted look of Turban Top Shells – Gibbula magus (Linnaeus). I found loads of them on Weymouth Beach recently. I was surprised to find them there because usually I find only Slipper Limpets. The Turban Tops were all sorts of sizes and conditions. Some were intact with beautiful red zig zag stripey patterns. Others were worn, broken and faded. Many were covered in a strange organic-looking textured reddish-brown coating. 

At the top of the sandy shore there were low-lying mounds concealing an old strandline of accumulated detritus that included large quantities of well-rotted seaweed. Winter waves had been eroding these deposits away and releasing the buried Turban Tops. The whole process was being speeded up by numerous pairs of large black crows that were systematically searching the beach for food. The bird pairs had divided up the territory and were leaving no piece of debris unturned in their patch.

There are earlier posts about these shells and the animals that occupy them. Click here for more information about Turban Top Shells in Jessica’s Nature Blog.

Side view of a Turban Top Shell with red pattern from an old buried strandline at Weymouth, Dorset, UK - part of the Jurassic Coast (2) 

The underside and aperture of a red patterned Turban Top Shell from a buried strandline on Weymouth Beach, Dorset, UK - part of the Jurassic Coast (3) 

An assortment of Turban Top Shells, mostly showing the underside, from a buried strandline beneath the sand at Weymouth, Dorset, UK - part of the Jurassic Coast (4) 

An assortment of Turban Top Shells, mostly showing the apices and spiral whorls, from a buried strandline beneath the sand at Weymouth, Dorset, UK - part of the Jurassic Coast (5) 

Paired black birds picking over the organic debris on the strandline on a particularly dismal winter day at Weymouth , Dorset, UK - part of the Jurassic Coast (6) 

Revision of a post first published 6 February 2010

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Stone Sunstars at Lyme Regis

Sunstar stone from Lyme Regis, Dorset, UK, on the Jurassic Coast (1)

These intriguing star-shaped or sun-shaped patterns found in boulders on the beach at Lyme Regis in Dorset are not fossils. At first glance, the distinct and clear designs look very much as if they would be. They are found in rounded boulders 60 – 90 cm across and are similar in size to the many large fossil ammonites that lie embedded in rocks all over the shore.

I thought when I originally discovered some, many years ago, that they looked like giant fossil starfish or jellyfish but knew that was impossible. The dark, roughly textured, radiating and circular lines of each pattern contrast with the smoother, paler rock in which they occur. The details of the patterns are different in each example. The patterns only seem to occur in slightly flattened boulders with an approximately rounded outline.

The patterns occur naturally in the boulders as a result of a geological process that I admit I do not fully understand. As far as I can make out, these sunstar-patterned boulders are calcareous concretions called Birchi Nodules that have fallen from strata high in the cliff that backs onto the seashore. They originate in a layer called the Birchi Nodular Bed on top of the stratum known as Shales-with-Beef. They are encased by a fibrous type of calcite known as ‘beef’. It is the ‘beef’ that forms the patterns in the outer layer of the nodule. The rocks date from the Lower Sinemurian of the Lower Lias in the Jurassic Period of about 190 to 200 million years ago.

To learn more about Birchi Nodules and Shales-with-Beef, I recommend that you refer to Lyme Regis – East to Charmouth, from Geology of the Wessex Coast of Southern England by Ian West, which is an extensive discussion of the geology of Lyme Regis in an on-line guide. This internet site is a virtual mine of local geological information to a fairly high level of complexity, with extensive referencing and illustration with photographs, diagrams, and maps both ancient and modern. 

Sunstar stone from Lyme Regis, Dorset, UK, on the Jurassic Coast (2)

Sunstar stone from Lyme Regis, Dorset, UK, on the Jurassic Coast (3)

Sunstar stone from Lyme Regis, Dorset, UK, on the Jurassic Coast (4)

Sunstar stone from Lyme Regis, Dorset, UK, on the Jurassic Coast (5)

Sunstar stone from Lyme Regis, Dorset, UK, on the Jurassic Coast (6)

Sunstar stone from Lyme Regis, Dorset, UK, on the Jurassic Coast (7)

Sunstar stone (with walking stick to show scale) at Lyme Regis, Dorset, UK, on the Jurassic Coast (8)

Sunstar stone amongst the other boulders on Monmouth Beach at Lyme Regis, Dorset, UK, on the Jurassic Coast (9) 

Revision of a post first published 3 May 2010

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