A Galway Shore – Part 1

A seaweed covered shore on the edge of Galway Bay

A cold and rainy day in March saw me exploring a beach on the west coast of Ireland in Galway Bay, between Galway City and Salthill.  Braving the inclement weather were joggers, plugged-in to headphones and clutching water bottles, as they ran along the promenade at the top of the shore. One or two individuals strolled with raincoats flapping and umbrellas braced against the wind. I had the seashore itself more-or-less to myself.

It is a sheltered, gently sloping, sandy shore where coloured pebbles accumulate at the top of the beach. Line after line of boulders, like loosely constructed groynes, stretch from high to low water mark dividing the shore into sections. They remind me of the stone walls that seem to proliferate in countryside and hill slopes all along this coast. Each beach section is like a field where mid- to low-shore rocks anchor a crop of seaweed – a profusion of vegetation that drapes each boulder and spreads out to blanket the surrounding sand.

The cloud-filled sky and persistent rain make the beach seem, from a distance, dull, almost monochromatic and melancholic – but that is an illusion. Close up, the limestone and granite pebbles provide a mosaic of many colours, intensified by the wetness. The seaweeds are made up of many types with a range of hues. Golden yellow fruiting bodies, and fronds in shades of olive, mark out the dominant Egg Wrack (Ascophyllum nodosum). Finely-branched red Wrack Siphon Weed (Polysiphonia lanosa) contrasts with the Egg Wrack on which it grows epiphytically.  Darker greens and browns are typical of the smaller Bladder Wrack (Fucus vesiculosus). Short curling clumps of greenish-yellow early-stage Channel Wrack (Pelvetia canaliculata) are distinct. Both limpet shells and mussel shells show patches of dark brown encrusting algae (probably Brown Limpet Paint, Ralfsia verrucosa). The seaweeds splash colour across rocks, pebbles and sand. – and the rocks themselves originate from different locations, sedimentary or igneous, with their own subtle colouring, texture and patterns.

How different this scene must look when the tide is in and the seaweed can float upright and sway in the waves. It really must look like an underwater field. The Egg Wrack (growing up to a metre and a half long) has egg-sized and egg-shaped air bladders, one formed every year along each frond, to aid buoyancy. The much shorter Bladder Wrack has small rounded air bladders in pairs either side of the midribs to help it float.

When the intertidal shore is submerged, acorn barnacles (Cirripedia) and edible mussels (Mytilus edulis) attached to the rocks can filter food particles from the water. The huge numbers of large limpets and common periwinkles living amongst and feeding upon the seaweed, and grazing red and yellow biofilms that encrust the rocks, can move far more easily and for greater distances when buoyed up by water and there is no danger of dessication – although they can be active when exposed to air at low tide if conditions remain cool and moist.

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Rocks and Pools on Burry Holms

The fantastically sculptured Carboniferous limestone around the tidal island of Burry Holms, which lies at the northern end of Rhossili Beach on the Gower Peninsula in South Wales, provides a habitat for many intertidal species.

The exposed rocks between the highest and lowest tide levels are covered with a patchwork pattern of permanently attached dark mussels and pale acorn barnacles on which thousands of roaming dog whelks feed. Periwinkles and limpets graze on the algal films that cover the rocks and the shells. The curiously curving contours of the rocks supply numerous sheltered micro-habitats in the form of small hollows, crevices, gullies, overhangs, and pools.

Some of the pools are only just big enough to accommodate a couple of sea anemones and a few dog whelks. Some bigger pools are almost perfectly circular smooth basins dissolved into the stone, characteristically highlighted in summer by vivid green soft seaweeds concealing minute fish and multitudes of striped top shells and other gastropods. The occasional deeper pool  becomes a safe haven for clusters of common starfish and small shrimps; while wet overhangs and clefts display numerous beadlet sea anemones in a vast array of colours from pale khaki to bright red, together with rounded mounds of orange sponge.

All the organisms that live on the rocks in the inter-tidal zone contribute to the process by which the rocks are shaped. Frequently, this is done in a slow, subtle, and imperceptible way by the actions of epilithic and endolithic micro-organisms such as bacteria, fungi, algae, and lichens, and by the way these microscopic organisms are scraped from the surface and surface layers of the limestone by grazing seashore creatures.

Sometimes, the erosion is visible to the naked eye – as in the circular “home bases” that limpets have created by the continual grinding and wear of their shells against the rock as they settled in the same place each time after foraging trips; together with acid dissolution of the stone by their waste metabolic by-products. Another easily observable kind of bio-erosion damage is the burrowing activity of marine polychaete worms and boring bivalved molluscs. These small holes in rocks are often clustered in a band immediately above and below the water line of pools but also in any continually wet or damp grooves and channels. The overall persistent erosional activity of marine invertebrate organisms on intertidal seashore limestone over thousands and even millions of years contributes to the creation of fascinatingly sculptured karst topography like that seen around the island of Burry Holms.

COPYRIGHT JESSICA WINDER 2014

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Lyme 8

 

COPYRIGHT JESSICA WINDER 2014

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Limpets on rusty iron

Limpets on rusty iron (1) -  Living limpet (Patella sp.) attached to rusty iron seaside pier.

I like the appearance of rust and I’m always looking out for interesting colours, patterns, and textures in oxidising iron. A good place to look is the metalwork on seaside groynes and piers which are invariably corroded by seawater. I find it amazing that small seaside creatures like limpets settle in these seemingly inhospitable locations where they eek out a living by grazing the microscopic algae that coat the surfaces. In their turn, as the limpets cling on to these man-made objects, the shells become stained by the orange of the rust and the green of the algae so that they blend into the overall constantly evolving design.

Limpets on rusty iron (2) -  Living limpet (Patella sp.) attached to highly coloured, patterned, and textured rusty iron seaside pier.

Limpets on rusty iron (3) -  Living limpet (Patella sp.) attached to highly coloured, patterned, and textured rusty iron seaside pier.

Limpets on rusty iron (4) -  Living limpets (Patella sp.) attached to highly coloured, patterned, and textured rusty iron seaside pier.

Limpets on rusty iron (5) -  Living limpet (Patella sp.) attached to highly coloured, patterned, and textured rusty iron seaside pier.

Limpets on rusty iron (6) - Living limpet (Patella sp.) attached to highly coloured, patterned, and textured rusty iron seaside pier.

Limpets on rusty iron (7) - Living limpet (Patella sp.) attached to highly coloured, patterned, and textured rusty iron seaside pier.

Limpets on rusty iron (8) - Living limpet (Patella sp.) attached to highly coloured, patterned, and textured rusty iron seaside pier.

Limpets on rusty iron (9) - Living limpet (Patella sp.) attached to highly coloured, patterned, and textured rusty iron seaside pier.

Limpets on rusty iron (10) - Living limpet (Patella sp.) attached to highly coloured, patterned, and textured rusty iron seaside pier.

Limpets on rusty iron (11) - Living limpet (Patella sp.) attached to highly coloured, patterned, and textured rusty iron seaside pier.

COPYRIGHT JESSICA WINDER 2013

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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

COPYRIGHT JESSICA WINDER 2012

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Seven small rockpools at Winspit

A small rockpool at Winspit, Dorset, UK - part of the Jurassic Coast (1) 

Small rock pools are scattered across the rock ledge at Winspit. Some are shallow and others are deep. Some are on the general surface and others are embedded in rock clefts. Most are rounded in outline but a few are differently shaped.  Some of the pools shown here seem almost like the shape of an eye or a mouth.

The colours and patterns made by the various seashore creatures and seaweeds found in and around the rockpools make attractive natural arrangements and designs. The pools and their inhabitants are very decorative features on the seashore even if you do not know what everything is called. 

These are really remarkable rockpools and unlike any that I have seen before. The general surface of the rock in this location is covered with an almost continuous coating of encrusting calcareous algae. This is Lithamnion, usually pink or purplish, but in many areas here it is bleached-out and white. Patches of smooth black encrusting lichen, and microscopic green algae, are interspersed with the Lithamnion to form an irregular  background patchwork of colour.

The purple-tipped, grey-green tentacles of Snakelocks Anemones clustered en masse in some pools. Tufts of filamentous red seaweeds were dotted all over the place and seemed to have a penchant for settling like plumed feathers on the conical shells of living limpets. The arcticulated, calcareous, pink and white branches of Coral Weed created tufts in pools and extensive carpets on the flat rock surfaces.

Yellow Rough Periwinkles grazed the red seaweeds. The unusual green Velvet Horn seaweed was growing in some pools. A few pools had nothing but pebbles swirling round and around at the bottom – preventing any organisms from settling. The red Beadlet Anemones were such a dark colour they looked almost black. Altogether this small area of shoreline with its numerous rockpools is a most unusual-looking place.

Another set of odd-shaped rockpools is described in Cart tracks and square rockpools at Winspit ………and for more details about the weeds and invertebrate seashore creatures mentioned above, you can use the SEARCH BOX on the top right-hand side of the blog’s home page, or the INDEX OF CATEGORIES, to locateother postings on the subjects.

Almond or eye-shaped small rockpool at Winspit, Dorset, UK - part of the Jurassic Coast (2) 

Small round rockpool with nothing but pebbles at Winspit, Dorset, UK - part of the Jurassic Coast (3)

Small shallow rockpool with yellow periwinkles grazing on red seaweed at Winspit, Dorset, UK - part of the Jurassic Coast (4) 

Small mouth-shaped rockpool at Winspit, Dorset, UK - part of the Jurassic Coast (5) 

Small round rockpool at Winspit, Dorset, UK - part of the Jurassic Coast (6) 

Small round rockpool at Winspit, Dorset, UK - part of the Jurassic Coast (7) 

Revision of a post first published 8 December 2009

COPYRIGHT JESSICA WINDER 2011

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Tiny Tidepool 1

 

This short video clip shows two small limpets (Patella sp.), with shells colourfully adorned by a coating of microscopic green algae, and patches of pale purple encrusting calcareous seaweed (Lithamnion sp.). The underwater pair are jostling against each other in a tiny tidepool at Fall Bay, Gower, UK.

If you look closely, you can see short fine translucent tentacles which are the pallial gills protruding from the body all around the margin of the shells. These gills on the mantle skirt are usually hidden from view when limpets cling to exposed rocks at low tide. The manoeuvering of the limpets may be a preparatory behaviour for mating. Patella limpets have separate sexes but all hatch out as males and later may develop into female individuals. This is known as protandric hemaphroditism. Click here for more information about common limpets on the Marine Life Information Network

The Carboniferous Limestone rock outcrops on the beach have been eroded by the sea and weathered into thousands of scooped-out hollows that retain sea-water when the tide goes out. These pools are home to many seashore creatures and seaweeds. Most are entirely lined, as in this example, with a coating are the lilac/purple/grey Lithamnion calcareous seaweed. Small niches are occupied by other miniscule limpets, an edible blue-shelled common mussel (Mytilus edulis Linnaeus), and a dark red beadlet anemone -Actinia equina (Linnaeus). A single minute navy-blue arthropod Anurida maritima (Guerin) from the Neanuridae Family scuttles across the water on the surface film. 

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