Strandline Shells on Swansea Bay

Seashells on the beach at Swansea Bay

Shells drift lines on the beachSeashells in situ on Swansea Bay strandlines or drift lines are mostly tiny immature common cockle shells but there are many other species of bivalve and gastropod mollusc shells too. I noticed mussels, tellins, and oysters, winkles, top shells, netted whelks, sting winkles, slipper and common limpets, and I am sure there were many more types. There were seven drift lines of shells lying parallel to the water line and decreasing in the number of accumulated shells sequentially up the shore. Each line represents the highest reach of the sea on a series of subsequent falling tides that were decreasing in reach each time.

It was interesting to see that wave-worn pieces of black coal and dark clinker from industrial plants across the bay were scattered amongst the light coloured shells together with a fair number of burial-blackened periwinkles. Many of the shells were fragmented and the accumulations included the calcareous tubes of marine worms. It would be lovely next time to take a sample home and sort it through under a binoc. I am sure that it would reveal much more information.

Click on any image below to see the details in a larger version.

Sea Slater at Fall Bay

Ligia oceanica Linnaeus

Sea Slater or Bilge Bug on the rocksHigh on the dry rocks at Fall Bay in Gower I spotted this fine creature running across the surface. It has many common names: sea slater, bilge bug, littoral wood louse, for example, but it’s scientific name is Ligia oceanica Linnaeus. With a body length of up to 25 mm it is the largest north-west European oniscid isopod. I picked it up to have a closer look at the wonderful texture and markings on its hard segmented covering. The books say that it is a frequent inhabitant of crevices in the upper rocky shore above high water mark but I have only seen it myself a couple of times in my lifetime of mooching on seashores.


Hayward, P. J., and Ryland, J. S. (2017) Handbook of the marine fauna of north-west Europe, Second Edition, Oxford University Press, ISBN 978-0-19-954945-0, p 350.

Fishing at Fall Bay

People fishing from the amazing rock formation at Fall Bay on the Gower Peninsula in South Wales

People fishing from the rocks at Fall Bay on the Gower Peninsula are almost invisible in the amazing beachscape of giant sloping limestone slabs dipping into the sea.

A Banded Wedge Shell at Rhossili

Donal vittatus (Da Costa)

The beautiful orange-yellow paired valves of a Banded Wedge Shell, Donax vittatus (Da Costa), lying like a butterfly on the beach at Rhossili Bay. It is one of the most common bivalved molluscs on this stretch of shore and there are lots of the empty shells of this type on the strand line. They exhibit a range of colours and sometimes the inside of the shell is tinted a wonderful purple.

Barrel-mouthed Jellyfish at Rhossili

Rhizostoma octopus Linnaeus

Barrel-mouthed Jellyfish washed ashore on Rhossili Bay at the base of cliffs near Kitchen Corner, 27th August 2017. One of several seen on the beach yesterday, each one looking different in size, colour, and arrangement of the organs. This one was pale blue and the domed umbrella surface had become turned inside out. The main shot was taken at ground level and into the sun to show how the light was shining right through the jelly. The inserted thumbnail image shows the same specimen viewed from above.

On the Rocks at Fall Bay

I am familiar with the commonly occurring horizontal stripes of rocky shore zonation where organisms are distributed between the tide levels according to their tolerance of exposure to air – but I  wonder what influences the distribution and arrangement of different species of seashore creatures to result in the irregular patchwork pattern as found on the intertidal rocks at Fall Bay in Gower. The sloping flat surfaces of the limestone strata can be covered with a complete encrusting layer of mussels, limpets, and barnacles, organised by colour, shape, and size to make a patterned carpet.