Spider crab moulted carapace

Beach Finds at Rhossili Bay 1

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It is fascinating how beaches can vary so much even within a relatively short radius, in terms of the beach composition and the kinds of organism that inhabit it, and the types of debris washed ashore. Rhossili Bay where these pictures were taken is a beach miles long, just like Swansea Bay. Rhossili Beach is clean sand right down to the water’s edge and beyond, and there are rocky promontories at each end of the shore. The location is an exposed one. This compares with Swansea Bay, superficially alike but where the sand gives way to more muddy sediments from mid tide level down to the sublittoral, and the nearest hard substrates are the docks and Mumbles respectively at the east and west ends of the seashore. The location of Swansea Bay, at the landward base of Gower, is more sheltered than Rhossili at the extremity of the Gower Peninsula. Consequently, the range and identity of the molluscs, marine invertebrates, and seaweeds, differs in the two bays because of the varying environment and habitats available for exploitation.

8 Replies to “Beach Finds at Rhossili Bay 1”

  1. Thank you, Linda. The spider crabs collect in groups in pools beneath the cliffs, where it is relatively safe from predators, in order to moult the old shells that they have out-grown, and harden-up their new ones. They are very vulnerable when they are doing that. The numerous empty shells (carapaces and legs) wash up on the beach afterwards.

  2. Dear Jess, what I love about your blogs is that you have the proper names for the stuff you take photos of. I am often looking at stuff on beaches thinking that’s an interesting shell/rock/crab but I forget to go and look them up!!

  3. Thanks, Emma. I try to put the right name on things if I can. Sometimes it takes a bit more work than others but it helps to keep the little grey cells working.

  4. You are so right about the variation between what might otherwise have appeared to be similar beaches. As someone who is always looking at the tideline and shells in particular I am always surprised how different they can be – beaches often have a ‘signature shell’ in my mind. It is funny to see Pharus legumen in such abundance at Rhossili – a shell I hardly ever see! The other week I was on a beach covered in Glycymeris (dog cockles!) – and nothing else!

  5. It is even more interesting than that. At different times, completely different assemblages may appear on a given beach. I guess that has something to do with the season, the weather, the strength and height of tide, dredging activities offshore, winter storm surges and so forth. Endlessly fascinating.

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