An assortment of things that caught my eye while visiting the beach on Swansea Bay last August. A wide expanse of several miles with big skies. There are always a lot of seashells washing ashore or stacked up on the high tide strandline. Many cockles and mussels and other types too, including small cowries; with the occasional eroded bone or mermaid’s purse. This natural debris is frequently mixed up with small black nuggets of coal or slag from past local industries. A stream was crossing the shore at this particular location and I liked the way that the dull cloudy sky was reflected by the ripples in the clear water, emphasising the pattern..
Jessica's Nature Blog 
I thinking the first photo reminds me of a knitting pattern with large complex cables. And those piles of tiny shells remind me of the first time I visited Florida when I was about five years old, first time I had seen the ocean, and I remember walking over similar drifts of shells in my bare feet.
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I have often reflected on my contribution to shell reduction on my liminal crunches along the intertidal. You, as a woman (i hope I do not overstep the mark in assuming a gender identity here) of a sharp and focussed disposition possibly have an idea how long it takes for a seashell to render down and become available for reconstruction. I would think a whelk shell (at least the central spine) must take a fair few years but uninhabited barnacle shells appear to be surprisingly friable.
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The shoreline is always changing, lovely to look at.
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Thank you, Claudia. I am pleased that the images provide food for thought.
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Thank you, Emma.😊
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It is quite complicated to work out the rates of decomposition for various shells on the beach, Alan. I understand that there is quite a lot of fairly recent research on the subject. You are right, of course, that gastropods with their relative lack of predators, more robust shell construction, habitats generally away from the degrading effects of pebbles and gravel, tend to survive (at least in part – the central columella) for longer on the beach than the shells of bivalves. The big exception in the UK being valves of flat oysters which can be very strong and remain intact. I have read somewhere that the stouter shells rolling around on the strandline can survive for hundreds of years; I personally think maybe thousands. I have often wondered just how old are some of the oyster shells that I find on Rhossili beach in South Wales. Your question makes me want to find out more. I will let you know if I can find some useful recent references to update my knowledge. At the moment I am looking at an excellent book “Ecology & Palaeoecology of Marine Environments” by Wilhelm Schafer, published by The University of Chicago Press 1972, pages 151 – 166.
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Many thanks. Jessica, for your very thoughtful and considered reply.
I have often tried to read the debris in the inter-tidal, the unaccountable dispositions of seaweed and razor-shells, in the manner of a psychic tea-leaf reader. This morning on my walk I began to consider the shells as memento mori. When the moist spongy creature inside the shell is alive the shell is amazingly strong. But when that bland, seemingly shapeless creature inside dies the shell loses its resilience. Often quite rapidly. How is that strength conveyed to the outer shell?
How difficult it is to remove living barnacles from the hull of a boat. How quickly their little brochs disintegrate when no longer occupied.
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How does the mollusc shell lose its resilience once the creature that occupied it dies? How is the strength of the animal conveyed to shell in life? There is no really adequate short answer but the composition of the shell (as well as the structure and design) is a key factor in its strength and survivability. Shell, like bone, is comprised or organic and inorganic components. The mollusc secretes the shell continuously during its lifetime. There is, in effect, a trellis of proteinaceous material on which the calcium based crystals are arranged. The combination of the two types of material gives the shell strength. There are different shell building blocks (microstructures) in different species and even within one type of shell.
When the mollusc dies, not only the animal flesh decomposes but also the protein component of the shell starts to decay – very slowly in most cases. A study of the rate of decay of its proteins (or rather the amino acids of which they are composed) is used to determine the age at death for shells in palaeontology and archaeology, for example. (An older method uses radiocarbon dating, for example, 30 individual shells from a single core sample of shells from a shoreline location was found to contain a range of dates from 1959 to almost 4000 years ago).
When the protein part of the shell disintegrates, the shell is more likely to break and crumble. I have studied oyster shells from archaeological deposits dating from the last 2000 years and their condition is variable depending on the physical and chemical conditions of their burial, and also that of their subsequent retrieval and storage. The shell may survive and be excavated with the protein component still largely intact; but drying out over years in storage can lead to the shells eventually becoming friable, flaky and powdery.
Regarding the difficulty of removing living barnacles from the hull of a ship when the plates that protect the small animal are so relatively fragile, the answer lies in the manner with which they attach themselves. Barnacles use a special glue which is very strong and is not soluble in water. Its wonderful properties are being investigated with a view to using a synthetic version of it in the biomedical field.
Hope this information helps.
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Your precise and patient dedication to (among other things) the education of others is (among other emotions) humbling. Thank you once again and more particularly for your hyperlink to the Japanese research on barnacle glue.
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Thank you. 😊
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