Worm Casts at Pembroke Bay

Lug worm casts and blow holes on a sandy beach

Lug worm casts and blow holes were widespread over the low-tide sand at Pembroke Bay on the Channel Island of Guernsey when I visited in early October. They had a more scattered distribution and the casts were not so fine as those I have seen on other parts of the island at Rocquaine Bay and Cobo Bay. Two species of Arenicolidae have been recorded for Guernsey and I wonder if I have been looking at the burrows and traces of the two different types. Here on the beach at Pembroke Bay I think they could well be Arenicola marina (Linnaeus) whereas those I had photographed else where could be Arenicola ecaudata Johnston which prefers the rich mud between stones or in rock crevices at low water. Both types of cast are shown in the gallery below. Click to enlarge the images and see the descriptions.

A Walk at Rocquaine Bay

Follow in my footsteps with a virtual walk along beautiful Rocquaine Bay on the west coast of the Channel Island of Guernsey. It is protected by a long sea defence wall which has employed different construction techniques along its length; mostly using local stone but also with along stretch of reinforced concrete (probably originating from German occupation World War II fortifications). The beach is both rocky and sandy with some pebble patches. Seaweeds of every colour abound. Huge limpets with white shells cluster on the bright orange-spattered L’Eree granite bedrock while outcrops of monochrome microgranodiorite occur on the upper shore near Fort Grey. Marine worm casts cover the softer muddy sands. Streams flow across the shore, their clear shallow water reflecting sunlight from the ripple crests and creating shadow patterns. A small stone jetty looks marooned among the rocks and a multi-coloured carpet of weed. Small boats bobbing in the turquoise water, rusty buoys and chains half-buried in seaweed, and algae-encrusted mooring ropes add to the evidence for fishing and leisure boating activities.

Click on the first picture to view the images in the gallery in the sequence that they were taken during the walk.

Tube-worm Holes in Ringstead Chalk Boulders

Close-up of tube-worm holes in a chalk boulder

Pebbles and beach stones riddled with small holes are a common beachcomber’s find. These small burrows and borings in the stone are frequently made by marine worms. The worms themselves, and the mud and sand tubes in which they live within the burrows, are usually absent. However, on the water’s edge in many coastal locations, if you know where to look, it is possible to spot the burrows still occupied by the worms; this is usually in large and mainly immovable boulders, or in the bedrock of the beach platform, or the base of a cliff face. The worm itself is almost impossible to see because at low tide, when the rock is exposed to the air, it retreats into the tube and burrow. Though sometimes, apparently, its two palps or feelers can be seen protruding from the hole and waving around vigorously. I haven’t observed that myself so far.

Without microscopically examining the actual worms, it isn’t possible to say with a 100 per cent certainty what these worms are. Nevertheless, there are enough characters available to say that these are most likely to be marine polychaetes of the Spionidae, and probably one of the Polydora group, maybe Polydora ciliata (Johnston).

All the Polydora species make a U-shaped tube from small particles of mud, or whitish calcareous matter if they have been burrowing into calcareous algae, shell, or limey stone; all this is stuck together with secreted mucus. The tube is normally embedded in the burrow that it has excavated. There are two holes in the mud tube, one at the front and one at the back end – but they lie side by side because the tube and burrow are U-shaped. In the examples photographed here, many worm tubes are packed together, and there are instances where the chalk burrows have joined together and broadened out into deeper, less well-defined, depressions.

The method by which the worms create the burrows is thought to be an almost incidental process. The worms initially settle and manufacture their mud tubes in the shelter of slight cracks and crevices in rock or shell surfaces, or between sessile barnacles, or amongst soft algae in rock depressions, and other such places on the seashore where it always remains damp at low tide. The metabolism of the living worm leads to the production of slightly acidic waste. Over time, the seepage of these waste products gradually eats into and dissolves the rock or shell on which the worm tube lies, enabling the worm to retreat further and further into the safety of the substrate. The burrow formed like this reflects the shape of the U-shaped mud tube.


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Calcareous marine worm tubes on a flotsam hub cap

Mostly the keeled calcareous tubes of the Serpulid marine polychaete worm Pomatoceros triqueter with a few empty acorn barnacle shells and seameats or Bryozoans. These epibiont organisms had colonised an old plastic car hub cap that eventually washed up as flotsam on the beach. The animals themselves had long vacated the shells and tubes that remained encrusted on the plastic.


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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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Lug Worms at Whiteford Sands

Lug worm casts on the beach: Thousands of huge lug-worm casts (probably from the marine worm Arenicola marina Linnaeus), looking like a vast field of walnut whips, stretching as far as the eye can see at Whiteford Point, Gower, South Wales (1)

Lug-worm casts  extending like a vast field of walnut whips as far as the eye can see at Whiteford Point, Gower in South Wales. These casts are made by the marine worm Arenicola marina Linnaeus.

Lug Worm blow hole and cast: Blow hole and spiral cast of the marine polychaete Blow Lug or Lug Worm, most probably Arenicola marina Linnaeus, on the shore at Whiteford Sands, Gower, South Wales (2)

Blow hole and spiral cast of the Blow Lug or Lug Worm – each representing opposite ends of the U-shaped tube occupied by the worm in the sand.

Blow hole of the marine polychaete Lug Worm Arenicola marina Linnaeus in the shore sediments at Whiteford Sands, Gower, South Wales (3)

Blow hole of the Lug Worm in sediments of Whiteford Sands in Gower. The head end of the worm lies beneath this hole and the worm eats the sand in order to get nutrients from the detritus and micro-organisms that it contains.

The spiral worm cast of excreted sediments from the marine polychaete Arenicola marina Linnaeus, the Blow Lug or Lug Worm, at Whiteford Sands, Gower, South Wales (4)

The tail end of the worm lies beneath the spiral worm cast that is composed of the excreted sediments after they have passed through the worm’s gut.

In the picture below you can see from the widely spaced distribution of blow holes and worm casts that Lug Worms on the beach at Whiteford Sands are not so abundant as at Whiteford Point (illustrated at the top of this post)because the sediments are drier, more sandy, less muddy, and therefore with a smaller organic component.

Lug Worm holes and casts on the sand: The widely spaced casts and blow holes of Lug Worms, Arenicola marina Linnaeus, on the drier and sandier shore of Whiteford Sands, Gower, South Wales in marked contrast to the intense colonisation of wetter and muddier shore sediments by Whiteford Point (5)

Hidden from view, of course, are the burrows themselves. These can only be truly observed in a laboratory observation using a glass-sided tank. As we saw yesterday (post of 9 July 2011), these or similar worms and their burrows have been around for millions of years as evidenced by trace fossils such as those found in the Jurassic Arenicolites Beds at Ringstead on the Jurassic Coast.

For more pictures showing the living Lug Worm itself, and video clips of Lug Worms click here for the ARKive web site.

Revision of a post first published 1 May 2009


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