At Dogs Bay

Dogs Bay in Connemara has a wonderful white sandy beach composed of the tiny shells of microscopic one-celled creatures that live mostly on the mud of the ocean bed. These animals are called Foraminifera. When they die, millions upon millions of their calcium skeletons, bearing many chambers and holes, and not visible to the naked eye, wash ashore to form this unusual sand. This is such a rare occurrence that Dogs Bay beach is the only one composed of foraminifera in the northern hemisphere.

The bedrock of the land around this wonderful white sandy shore is made up of volcanic rocks including granite that has many different colour forms and patterns due to the different mineral crystals that it contains – if you get up really close to see it. The granite outcrops on the shores often have a rounded surface where ice sheets or glaciers passing over them have ground them smooth. The waterside rocks form attachments for a variety of seaweeds, along with many seashore creatures, particularly gastropod molluscs like periwinkles and limpets, whose brightly-coloured empty shells accumulate at the base of boulders low down in the intertidal zone.

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Moon Jellyfish Art

Swimming Moon Jellyfish

Slowly pulsating bells of Moon Jellyfish swimming near the surface of shallow water over seabeds of swaying seaweed.

Swimming Moon Jellyfish

Swimming Moon Jellyfish

Swimming Moon Jellyfish

Swimming Moon Jellyfish

These images were previously displayed on my other site Photographic Salmagundi; and on Jessica’s Nature Blog there is also a  short video of one of the slowly swimming Moon Jellyfish that were the subject of this artwork.

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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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A Masked Crab at Studland

A Masked Crab waiting for the tide to come in

I saw a little Masked Crab (Corystes cassivelaunus Pennant) on Knoll Beach at Studland the other day. It was an unusual sighting for that location. The crab was alive – but lucky to be so. It had buried itself in the wet sand to survive the rigours of exposure at low tide. There are not many other places for an animal to hide on this part of the beach.

The small crab, only a couple of inches long, would probably have stayed out of view until the tide came in again – except that this was the afternoon that several schools decided that it was just the right moment for the students to run on the beach while the sun was shining. The youngsters pounded their way along the shore and one of them stepped on the very spot where the crab was sheltering. Being disturbed by this close encounter, it surfaced, all covered in wet sand, as I walked past it and eastwards in the direction of Shell Bay.

I was surprised to see this same little seashore creature again as I made my way back along the water’s edge going westwards. I know it was the same crab because it was almost the only live thing I found, and certainly the most interesting. It was one of those days when there was not much at all newly washed ashore: a few fresh clumps of spindly red seaweed, some brown Sea Oak and strands of kelp, a few pieces of translucent green Sea Lettuce, and some clusters of Slipper Limpets. Lots of empty bivalve shells.

On this second meeting with the Masked Crab, the creature was more active and had got rid of the sand which had been covering it before. It was waiting for the waves. I have seen this activity previously in Masked Crabs on Rhossili Beach on the Gower Peninsula. The animal sits facing the sea, using its legs to brace itself against the oncoming water. Its two fringed antennae can be joined together to form a single tube and this was projecting forwards and upwards – looking very much like an angler holding a fishing rod. It was fascinating to watch the way to crab parted and then joined the antennae, moving them side to side as if using them to gauge the speed and timing of the next wave. The antennae form a breathing tube when the crab is buried.

I took a few photographs of the Masked Crab and some short video clips which you can see below. I hope that you will appreciate that it was a bit difficult to film the crab in action because of its small size and the necessity for recording it in such a low position – plus the imminent drenching of both the crab, the camera, and the photographer.

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Goose Barnacles at Ringstead Bay

I always like to find Goose Barnacles (Lepas anatifera) on flotsam at the beach. These strange creatures live attached to items that free-float around the oceans of the world; and we only see them when they wash ashore, as they did yesterday at Ringstead Bay in Dorset, England. Thousands of these strange marine creatures were clustered onto a tree trunk and its branches that lay freshly beached on the shingle. All the pebbles here seem to have returned now – it was only a week or so ago that they had all more or less disappeared following stormy weather.

Click here for more information about Stranded Goose Barnacles and Goose Barnacles on Rhossili Beach in Jessica’s Nature Blog.

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Handbook of the Marine Fauna of North-West Europe

Aside

This is an invaluable book that I regularly use.

 

The Handbook of the Marine Fauna of North-West Europe does what it says on the cover, and the Amazon reviews reflect its usefulness:

When Peter Hayward and John S. Ryland first published Marine Fauna of the British Isles and North-West Europe, it became an instant classic in the marine reference literature. Now with Handbook of the Marine Fauna of North-West Europe, the same editors offer a concise, practical guide to over 1,500 species from the major marine phyla-from sponges to fish-in a format that is ideal for field use. With its simple dichotomous keys, individual descriptions, profusion of illustrations, and extensive reference section, the book allows for rapid and easy identification of all but the rarest marine animals found on the sea shores and shallow sublittoral zones of the region. Students, researchers, and amateurs interested in zoology, marine biology, and ecology will all want to own a copy of this unique field guide.

“The essential guide for any aspiring marine biologist”, 16 Dec 2011
By Magnus Johnson (UK):

This is a core text that we use at the Centre for Environmental and Marine Sciences for our undergraduate courses in Marine Biology and Ecology. It is “the book” to use as a starting point and it is generally enough until you get to postgraduate level or need to specialise in a particular group of animals (it doesn’t cover algae obviously). For each group there is an introductory section that gives you a guided tour of body parts. This is usually followed by a key to families which is generally easy to follow once you have the taxa specific nomenclature in your head. Handy references to diagrams direct you examples of each family. Once you have identified your specimen down to family there is a key to species. For most taxa each species has a succinct description with details of their distribution and colouration that allows you to confirm your identification.

Common Piddocks – rock-boring molluscs

Common Piddock dorsal view

Here are some close-up photographs of the Common Piddock – Pholas dactylus Linnaeus (Mollusca; Bivalvia; Pholadacea; Pholadidae) showing details that are important for its specific identification. The specimen in the first three images still has the dead animal within the shells. This is one that I collected from those I found at Monmouth Beach in Lyme Regis (see the previous post) where a slab of shale, complete with the rock-boring molluscs still inside the burrows, had been thrown up on the shore by stormy seas. The empty shell shown in images 4 – 8 is a beach-worn specimen picked up on Knoll Beach at Studland a few weeks ago.

Although the length of the shell of the Common Piddock can be up to 15 – 24 cm or 6 inches, the examples shown here are smaller – with an  actual size of shell for the Monmouth Beach specimen of 50mm, and 108 mm in the shell from Knoll Beach.

Full details of the shell characters used for identification can be found in the references given below. This bivalve mollusc bores into sand, peat, marl, wood, shale, slate, chalk, limestone, red sandstone, schists, firm clays, and even thick old oyster shells, from low on the seashore to depths of a few fathoms. It occurs in The British Isles from Kent along the south and south-west coasts, including South Wales, and as far south as the Atlantic coast of Morocco. Of particular interest is the phenomena of phosphorescence or luminescence exhibited by the living animal which has has bioluminescent properties and glows with a blue-green light in the dark.

Earlier posts on Jessica’s Nature Blog that refer to the holes in rocks and pebbles made by piddocks and other seashore creatures include:

Rocks with holes made by Piddocks – Part 1

Beach Stones with Holes at Worms Head Causeway

Peat ‘pebbles’ with piddock holes

Pebbles with holes made by boring sponges

Pebbles with holes made by tube worms

Pebbles with holes made by sea creatures

Driftwood with holes made by Gribbles & Shipworms

Benjamin & the pebble full of holes

Shells with holes made by boring bivalves

A rocky beach near Portland Bill

REFERENCES

Tebble, Norman (1966) British Bivalve Seashells – A Handbook for Identification, published for the Royal Scottish Museum by HMSO – Edinburgh, 2nd Edition 1976, ISBn 0 11 491401 X, pp 175 – 180. [Out of print but now available on CD from Pisces Conservation Ltd.]

Hayward, P. J., & Ryland, J. S. (Eds.) (1995) Handbook of the Marine Fauna of North-West Europe, Oxford University Press, 1998 reprint, ISBN 0 19 854055 8 (Pbk), pp 619 – 622. Still in print and available from Amazon and other booksellers.

MarLIN about Pholas dactylus

Wikipedia about Pholas dactylus

World Register of Marine Species about Pholas dactylus

Marine Species Identification Portal – about Pholas dactylus

Common Piddock right side view

Common Piddock ventral view

Common Piddock exterior view left valve

Common Piddock exterior view left valve

Common Piddock anterior end left valve

Common Piddock interior view left valve

Common Piddock shell showing umbonal reflection

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Rocks with holes made by Piddocks – Part 1

It is common to find pebbles and rocks which have holes in them when you walk on the seashore. These holes are frequently the result of various marine invertebrates that have burrowed into the rock. The larger, nearly round, holes about a centimetre or so across are often made by bivalved molluscs called Piddocks – these have a special shells and processes for mechanically boring into the rock.

Most commonly, you find stones, or shells, or bedrock, with holes – but the inhabitants have long disappeared. Other times, you glimpse the shell within the burrow but removing it is very difficult to do without totally destroying the shell. If you are really lucky, then you might spot a colony of living piddocks in their burrows at the lowest point of the tide where they will be sporadically squirting water out of their protruding siphons.

In any event, it is quite difficult to see all the details of the shells and thereby identify the creatures to species. Shells that occasionally get washed up on the beach may be abraded and worn, and vital parts for identification are always missing. So, I was delighted last Sunday to see slabs of broken shale, complete with piddocks in burrows (albeit dead specimens), washed up on the shingle of Monmouth Beach in Lyme Regis which is in Dorset, England.

This provided a wonderful opportunity to see what these boring bivalve molluscs and their shells really look like and observe the particular shell features that adapt the organism for this strange lifestyle – but which are normally missing from beach worn specimens on the strand-line.

As far as I can make out, all the specimens that I photographed on the beach were the Common Piddock (Pholas dactylus). I took a few home to clean them up and photograph them in better conditions. The light at the time was very poor, winds were very strong making it a problem to keep the camera still, and the air was laden with salty moisture that persistently misted the camera lens. I’ll show the photographs I took at home in the next post. Meanwhile this post will focus on the piddock shells in situ.

The shell of the Common Piddock is elongate, roughly elliptical and can grow up to 150 mm long – although the specimens I saw were a lot smaller. The anterior (front end) of the shell has a strange beaked appearance and surrounds a permanent pedal gape through which the muscular foot can be extended. The surface sculpturing at the front end of the shells consists of many short, sharp spines that develop at the junctions where the concentric ridges of the valves intersect with the radiating ribs. The spines enable the mollusc to use the shell like a rasp to file away the rock (or shell, or wood, or peat) as it bores down and creates its personalised living accommodation within the protective confines of the substrate.

This boring mechanism is aided by several extra features of the shell – accessory plates on the outside and a long curved process called the apophysis on the inside. The external accessory plates are the paired protoplax, the paired mesoplax, and the single metaplax. Rhythmic contractions of the muscles attached to these plates, and to the apophysis, enable the mollusc to perform a twisting action that aids the drilling process. The whole procedure is further enhanced by a forcing outwards of the two valves against the rock walls using hydrostatic pressure (sucking water in through the siphon and holding it  temporarily to create pressure).

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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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Link

I really want you to have a look at the fantastic work of Thierry Alexandre. He not only paints and makes wearable art but also creates performance art. On his website you can see both still images and videos. The seashore provides him with much of the inspiration for the creations, often incorporating seashells and other flotsam for the costumes. The video at the top of this post shows a costume made with oyster, mussel, whelk and slipper limpet shells, adorned with cuttlefish bones and spider crab carapaces – to mention just some of the strand-line items. Incredibly innovative work. I particularly like the images where he is on the beach coated head to toe with glutinous clay to which gravel is adhering – rather like the clay ball from Ringstead Bay which I photographed some time ago.