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.

10 thoughts on “On the Rocks at Fall Bay

  1. Love the close-ups of the mussels etc. I don’t know how that pattern is formed but somehow feel if look at it long enough a logical answer ought to come.

  2. Yes, it is an interesting phenomenon and likely to be the result of a combination of many factors. Fall Bay has an amazing display of rocks which comprise vast, over-lapping, flat-surfaced slabs of limestone sloping down to the sea. Each slab has a slightly different composition and is exposed to different environmental conditions that affect the colonisation of the surface by marine organisms.

  3. Thank you, Angela. I think there are many factors interplaying to produce the patterns of animals on the rocks. At Fall Bay there is a series of massive overlapping slabs of limestone. They were all formed during the Carboniferous Period but each layer was laid down under different conditions so that each has its own composition and texture. Some would be more suitable for encrusting organisms than others. The colonisation of the rock slab by marine organisms might depend on the surface texture; its height above Chart Datum (sea level); the degree of exposure to wind, waves and currents; seasonal and annual environmental fluctuations; reproductive cycles of the animals; and the sequence of colonisation by the immature stages of the organisms. Some slabs of rock have no attached organisms. Some slabs have just limpets in the nooks and crannies. Others have limpets and barnacles, and a few have mussels as well. It seems possible that in the photos shown here the limpets were the first to gain hold. Barnacle spat settlement followed next and was most successful on and around the limpets. The young mussels arriving afterwards occupied the remaining space around the limpet and barnacle “nuclei” on the rocks. Its a theory, anyway.

  4. I am not certain about that. If you look at my replies to comments that other people have made, you will see that I am thinking the pattern has more to do with the sequence in which the rock surface is colonised and the environmental conditions affecting the settlement area.

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