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.
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.
You don’t exactly have to keep your nose to the ground to see them but you do have to be a keen observer to notice all the different tracks and trails left on the soft wet sediments of the beach at low tide. Larger marks left by people and vehicles are the first ones you see. Bird footprints are every where. The birds are feeding on all sorts of invertebrate seashore creatures like worms, small crustacea and molluscs – all of which leave holes, burrows and furrows as they move in and out of the sand and across the surface. Some of the pictures shown here simply aim to give the general context for the area of Whiteford Sands that I was walking across. If you look closely the other images, you will see not only the ripples in the sand but also the intricate network of traces left by the virtually invisible organisms that inhabit this ecosystem. The larger furrows in photos 1, 12 and 13 are made by the common winkle (Littorina littorea Linnaeus). I cannot name each animal that is responsible for each of the other types of trace. However, I am sure that there will be some specialists out there who could, especially those researchers concerned with the interpretation of trace fossils (the ichnologists).
Click images to view full size.
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.
Revision of a post first published 2 December 2009
COPYRIGHT JESSICA WINDER 2011
All Rights Reserved
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.
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 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 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.
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
COPYRIGHT JESSICA WINDER 2011
All Rights Reserved