Rocks and Pools on Burry Holms

Mussels, barnacles, and dog whelks on eroded limestone at Burry Holms

Beadlet anemone

Seashore creatures on eroded limestone at Burry Holms

The shallow circular depression of a limpet “home-base”.

Marine worm burrows in limestone at Burry Holms

Sea anemones and Dog Whelks on the rocks at Burry Holms

Small seaweed-filled rock pool at Burry Holms

Detail of the area around a rock pool showing small burrows made by marine polychaete worms and larger holes made by burrowing bivalved molluscs.

Small hollow in the karstic rock surface filled with water and bright green algae

Small hollow filled with water and bright green algae in the an eroded rock surface covered with mussels and sessile barnacles on the island of Burry Holms.

Seashore creatures clinging to eroded limestone rocks at Burry Holms

Sea anemone in a rock pool at Burry Holms

Near perfectly circular rock pool eroded into the limestone at Burry Holms.

Sea anemone, sponge and seaweed on the rocks at Burry Holms

Seashore creatures attached to a rock overhang at the edge of a small algae-filled pool in the eroded limestone surface at Burry Holms

Pattern of dark mussels and light barnacles on bio-karstic rocks

Bright orange sponges with dog whelks in a damp rock cleft

Limpet shell completely covered by acorn barnacles.

Sponge, sea anemones and dog whelks in a mini rock pool

Small seashore creatures encrusting the eroded limestone of Burry Holms

Congregation of Common Starfish Asterias rubens in a rock pool at Burry Holms

Sea anemones on the rocks at Burry Holms

Cluster of small seashore creatures in a damp rock hollow at Burry Holms

Sea anemones on the rocks at Burry Holms

Cluster of dog whelks sheltering in an eroded groove in the limestone on the east side of Burry Holms

Small algae-filled pool surrounded by a patchwork of small seashore creatures encrusting the rock

Sea anemones on the rocks at Burry Holms

Mussels, barnacles, and dog whelks on eroded limestone at Burry Holms

Sea anemones on the rocks at Burry Holms

Common Starfish under surface

Close-up of marine worm burrows in limestone at the waterline of a rock pool on Burry Holms

Sea anemones and dog whelks in a rocky hollow at Burry Holms

Bright red Beadlet Anemone with dog whelks and barnacles

Small rock pool in eroded limestone surface at Burry Holms

Detail of bio-eroded area of marine worm burrows on the waterline of a small rock pool in Carboniferous Limestone

Small rounded rock pool in limestone at Burry Holms showing bio-erosion

Sea anemone on the rocks at Burry Holms

Marine worm burrows in limestone around the water line of a rock pool

Large calcareous basal plate of a Perforatus Barnacle that has been knocked off the rock, with newly-settled barnacles of a smaller species

Barnacle-encrusted limpets clinging to High Tor Limestone at Burry Holms

Common Starfish upper surface

Near perfectly circular rock pool eroded into the limestone at Burry Holms.

Seashore creatures on eroded limestone at Burry Holms

Sea anemone and Dog Whelks on the rocks at Burry Holms

Sea anemones clinging to rock at low tide on the island of Burry Holms

Common periwinkle sheltering in an empty Balanus perforatus barnacle shell

Sea anemone on the rocks at Burry Holms

The stout curved beak-like opercula plates of a living Balanus perforatus barnacle on rocks at 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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