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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Up-date on the multi-coloured rock pool at Rhossili

Rock pool recovering from plastic pollution in October 2009. The water is fairly clear. (1) 

Previously I have talked about a small rock pool at Rhossili that had filled up  with  multi-coloured pieces of plastic probably arriving at this one small area of the beach from hundreds, even thousands, of miles away. Bright coloured fragments and pellets of plastic were also observable in the regurgitated remains spewed up by seabirds on the beach. That was back in the summer 2009. I have been keeping an eye on the pool to see what its fate might be.

Rock pool recovering from plastic pollution in October 2009 (2) 

By October 2009, high tides seemed to have mostly cleaned out the pool and it looked on the road to recovery.

The rock pool filled again with plant remains and plastic by winter seas. January 2010 (3) 

By January 2010 the pool was contaminated again. However, a large proportion of the rubbish in the pool this time was organic. Vegetable remains included straw-like terrestrial plant stems, broken fronds of brown seaweeds, and the large air bladders of Egg Wrack.

For earlier postings related to the plastic pollution in this pool, click here Multi-coloured Rock Pool at Rhossili and More about the multi-coloured rock pool at Rhossili.

Plant remains and plastic rubbish trapped again in the pool over winter. 1 January 2010 (4) 

Plant and plastic rubbish trapped again in a high rock pool over winter. 1 January 2010 (5) 

Revision of a post first published 19 January 2010

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Green Leaf Worms at Spaniard Rocks, Rhossili

Green Leaf Worm, Eulalia viridis (Linnaeus), on mussels and barnacles encrusting limestone cliffs at Spaniard Rocks, north end of Rhossili Bay, Gower, South Wales.UK (1)

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.  

Green Leaf Worm habitat - Spaniard Rocks, Rhossili, Gower, encrusted with red seaweed, mussels and barnacles in April 2009 (2)

Home of the Green Leaf Worms - rocky shore zonation of Carboniferous limestone at Spaniard Rocks, Rhossili Bay, Gower - showing successive colonisation of the surface by various organisms at different heights above sea level (3)

Green Leaf Worm, Eulalia viridis (Linnaeus), on mussels and barnacles encrusting limestone cliffs at Spaniard Rocks, north end of Rhossili Bay, Gower, South Wales.UK (4)

Revision of a post first published 8 May 2009

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Sea Spurge on Llangennith Burrows, Rhossili

Sea Spurge, Euphorbia paralias Linnaeus, on the sand dunes of Llangennith Burrows backing onto Rhossili Bay, Gower, South Wales, UK (1) 

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.

Sea Spurge, Euphorbia paralias Linnaeus, on sand dunes of Llangennith Burrows backing onto Rhossili Bay, Gower, South Wales, UK (2)

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.

Sea Spurge, Euphorbia paralias Linnaeus, on sand dunes at Llangennith Burrows backing onto Rhossili Bay, Gower, South Wales, UK (3)

Revision of a post first published 10 May 2009

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Strandline dogfish at Whiteford Sands, Gower

Lesser Spotted Dogfish or Rough Hound, Scyliorhinus caniculus (Linnaeus), on the strandline at Whiteford Sands, Gower, South Wales, UK (1)

The Lesser Spotted Dogfish or Rough Hound, Scyliorhinus caniculus (Linnaeus), found on the strandline at Whiteford Sands, Gower. The photograph above illustrates the most important feature for distinguishing this species from the Large Spotted Dogfish or Nurse Hound, Scyliorhinus stellaris (Linnaeus).

In the Lesser Spotted Dogfish as shown above, the nasal flaps, the skin that extends from the nostrils down to the upper lip, describe a smooth continuous curved groove down to and along the lip line. In the larger Nurse Hound, the nasal flaps and nostril grooves turn away from the mouth and the outline is approximately W-shaped.

Lesser Spotted Dogfish, Scyliorhinus caniculus (Linnaeus), on the strandline at Whiteford Sands, Gower, South Wales, UK (2)

The Lesser Spotted Dogfish is cartilaginous rather than bony and very shark-like because it is related to that group of fish. You can see the small sharp teeth on the lower jaw; in fact, these are denticles in the skin rather than ‘proper’ teeth embedded in the jaw bone. The rough skin covering the whole animal contains thousands of similar but microscopically small versions of the teeth in the mouth.

Lesser Spotted Dogfish, Scyliorhinus caniculus (Linnaeus), on the strandline at Whiteford Sands, Gower, South Wales, UK (3)

The Lesser Spotted Dogfish grows upto 75  cm long compared with1.5 m long in the Nurse Hound. It is common and lives on sand or mud in shallow water. (The Nurse Hound likes rocky ground in shallow water). It is considered to be quite tasty (when fresh) and is the fish that used to be called  ‘rock salmon’ and sold in fish and chip shops.

Finally, a view of the Lesser Spotted Dogfish showing the darker colouring of the upper and side surfaces with the characteristic spot markings.

For more information on the Nurse Hound see the information page on this blog. 

Lesser Spotted Dogfish, Scyliorhinus caniculus (Linnaeus), on the strandline at Whiteford Sands, Gower, South Wales, UK (4)

Revision of a post first published 12 May 2009

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Pennant’s Swimming Crabs on Rhossili beach

The small crab Portumnus latipes (Pennant) emerging from the wet sand at low tide level on Rhossili beach, Gower, South Wales, UK (1)

Emerging largely un-noticed from the wet sand at low tide level at Rhossili Bay, Gower Peninsula, this small crab seems to be pushing up at least its own weight in sand.

Rinsed off in some standing water on the shore, you can see a few more details which allows me to suggest it is Pennant’s Swimming Crab, Portumnus latipes (Pennant).

The living crab Portumnus latipes (Pennant) found on the lower shore at Rhossili Bay, Gower, South Wales, UK (2)

This crab lives on the sand at low tide level and in the sublittoral up to a depth of 150m. It frequently buries itself in the wet sand to a depth of a couple of centimetres – as this individual had done to protect itself when the tide was out.

The crab in the two pictures below didn’t survive its burial in the sand; perhaps trodden on by one of the many surfers who use this stretch of the beach. However, its demise makes it possible to demonstrate the diagnostic features of the species more clearly.

The small crab Portumnus latipes (Pennant), deaceased, upper surface, on the sand at Rhossili Bay, Gower, South Wales, UK (3)

The carapace is about 2 cm long and it is slightly elongate and heart-shaped, reddish with white mottling. Between the eyes there are three blunt ‘teeth’ of which the central one is a bit longer. The front claws of chelipeds are more or less the same size and are usually held under the carapace. The back legs end with a flattened leaf-shaped or spear-shaped segment or pereopod that acts like a paddle to help it swim.

You can find more information about Pennant’s Swimming Crab and other British crabs on the Glaucus web site.

The small crab Portumnus latipes (Pennant), deceased, under surface, on the lower shore sand of Rhossili Bay, Gower, South Wales, UK (4)

Revision of a post first published 13 May 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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