Shells

Swansea beach is crunchy with shells, and that means that the waters are pulsating with life. Other nearby beaches, less so. Why so many in Swansea? Shellfish eat stuff. What stuff? The stuff they eat determines the colour of the shell. Other stuff eats shellfish. Who they? Yet other stuff eats the stuff that eats shellfish, and so on.

But it’s all out of sight, beneath the water. The shells are the marine population’s equivalent of pizza boxes discarded after a Friday night of revelry, every night being Friday night down there.

I have grandchildren currently hiding indoors as Covid-19 stalks the hills scenting their blood, while schools bar their doors to tiny hammering fists to better protect them from illness and their staff from responsibility. But when that has been resolved, I’ll invite them (the grandchildren) to the beach to find one examplar of each type of shell. Mr Google and I will then photograph and identify each shell and begin to piece together the assault plan which fails daily while leaving billions of broken bodies scattered over the tide line.

Molluscs vs Climate Change.

Carbon dioxide accounts for 415 parts per million of the atmosphere, 0.0415%, and even that level is a cause for concern given that the figure was 280 parts per million in 1850 and climate change is attributed to the rise. But 150 million years ago the figure was 2500 parts per million, and 400 million years prior to that it was around 6000 parts per million. So where did it all go?

Molluscs (such as whelks), crustaceans (such as crabs), plankton (the offspring of molluscs and crustaceans) and coral have learnt to combine calcium and carbon dioxide dissolved in the water to produce protective shells. Time and gravity compress these shells into limestone and their organic contents into oil and gas.

So shells and limestone are carbon sinks that contains around one hundred million billion sequestered tons of the stuff, 2400 times more than the combined free carbon circulating between the atmosphere, oceans, plants and soils. And if all that were still in the atmosphere, how hot would it be?

Whelks

In the meantime, consider this table, taken from the Swansea Rural Local Development Strategy:

FLAG stands for Fisheries Local Action Group. The Swansea Bay FLAG covers the 70-mile stretch of coastline from the Loughor estuary in the west to Porthcawl in the east.

Anyone who has ever walked along Swansea beach knows that they are common enough, and the above table indicates that they are edible. But Swansea whelks are not eaten in the UK or even in Europe: all sales – nearly £50,000 worth – are to the Far East. Proof positive that we can’t even run a whelk stall. Can they be found in Swansea market?

And The Rest

I had hoped to bribe my grandchildren to retrieve an exemplar of every shell type on the beach whilst I supervised from behind a capuccino and chocolate brownie, but my daughter furloughed them instead and it all fell to me. Plus ça change. I have had to guess what each of the following shells might be:

Netted Dog Whelk

Found crawling over stones and gravel in pools on the lower shore, these driller killers feed on other shellfish. They have a toothed proboscis – the rasula – that they use to drill through the shells of their victims and then rasp away at the flesh beyond.

Cockle

Usually buried in shallow sand but can be found on the surface at low tides. Staggeringly common – there may be 10,000 juveniles per square metre.

This is, I think, a Spiny Cockle – it could be a smaller Prickly Cockle – and not to be messed with. It seems to live further west than its more refined Swansea cousins – I found it on Pendine sands and at Llangenith. Not a cockle to turn your back on. How it works blind from the inside to create such an intricate three-dimensional pattern beats me. Spiders’ webs are only two-dimensional and spiders have eyes to help them.

American Slipper Limpet

Accidentally introduced into Europe from Amreica in 1887 and now very common. And weird. I quote from a Collins seashore guide:

‘Several specimens are usually found heaped one atop the other, forming chains of two to ten or more individuals. The largest (lowermost) member of the chain will be female, the outermost, smallest will be male, and those in between will be in the process of switching from male to female.’

Toothed Top Shell

There are many varieties of top shell so I’m going out on a limb when I assert that this is a Toothed (or Thick) specimen. The top of the shell gets worn away to reveal the pearliness beneath.

Flat Top Shell

I really am guessing this time, but it’s smaller (up to 13mm high) than the Toothed top shell (up to 30mm high) and it has clear non-zigzagged bands of colour.

It’s larvae settle onto rocks after a few days of being on the plankton menu enjoyed by the larger lifeforms.

Common Periwinkle

Grazes on algae growing on rock surfaces. It can be cooked and eaten, using a pin to fish the flesh out, then (childhood memory) discarding it because of its resemblance to a recently picked bogey. We were young and not that hungry.

Common Mussel

From the middle shore downwards, mussel beds can contain millions of creatures, each one roped by strands of bysuss – secreted from its bysuss gland – to rocks using threads that pass out between the two halves of the shell

Common Limpet

These use their powerful foot to cling to a rock and, at high tide, venture out to graze algae from the rock surface before returning to their starting point, a contoured niche that exactly fits their shell.

My wife once kicked one off a rock and ate it raw. We divorced shortly thereafter.

Razor Shell

A very poor specimen: I’ll keep my eyes open for a better one.

Huge numbrs of these creatures burrow in the sand of the lower shore, protruding a short siphon at high tide to feed and breathe.

Common Oyster

Stocks of this have declined significantly in recent years, but not in Swansea: the shore is covered in their shells. I don’t understand the structure of the shell – it has several layers, as if the creature is constantly building a new, longer ceiling below the previous ceiling as its body length increases.

Thin Tellin

These live below the sand , extending two long siphons – an inlet and an outlet – for feeding and respiration. Up to 28mm long, its colour is determined by its diet.

Rather than extract nourishment from the water and hence enjoy a constantly replenished food supply, it uses its siphon to poke through the sand in which it is buried and hoover crumbs of deposited organic matter from the sand on the sea bed. And when it has eaten it all, it needs to move to another site. Hence the shell is very smooth, offering little resistance as it pushes through the sand.

Tellin, Spisula and Donax

Tellin or Spisula? I asked someone and they replied ‘That would be Tellin’, but I think they’re Spisula.

Or Donax? I asked ‘Spisula, Tellin or Donax?’ and they snapped back ‘Donax, just Donax’ before I even finished the question, so they must have been confident.

Spisula? Donax? That would be Tellin.

Necklace Shell

Possibly (‘up to 3cm high, shell more or less globular, with a rather stepped, conical spire’). If so, a lower-shore sand-dwelling carnivore that feeds on tellins.

Tellina

Maybe. The big one in the middle. There are several types of Tellina, and many shells that look something like this – some more ridged than others, some shinier than others, some with a white inner shell, some more of a yellow and so on.

Common Saddle Oyster

The flattest of all bivalves, they cling to rocks and bling in the sun when exposed.

Quahog

A big fella, around 10-13cm across, with marked growth lines. Widespread but rare, I’ve only ever seen the two specimens on Swansea beach. It likes mud, which explains why it would feel at home there.

One of the longest-lived animals on the planet, scientists in 2013 estimated that it may live for more than 500 years.

Something Oystery

But not sure what.

Scallops

There are several types of scallop and I’m not going to risk identification of the individual specimens in the photo other than to speculate that the top shell is an example of a variegated scallop.

Which makes it gender fluid. It matures as a male, but then swaps several times between male and female during the course of its life.

Thick Trough Shell

A thick, ridged shell, up to 50mm long, brown when alive but then gradually loses its colour. Another filter feeder.

Pidock

Piddocks burrow into mud, timber and even into rocks. They can grow up to 10cm in length, but the examples I found are less than half of that. I suspect they are the smaller Atlantic mud-piddock, Barnea truncata, often referred to as the fallen angelwing, growing up to 5.7 cm long.

They possess a white exterior and interior and burrow into mud, clay or softwood: I found the ones in the photo inside an old wooden jetty strut. The fragile shell crumbles easily so is rarely dug from mud without it breaking.

One of the piddock’s shells has a set of ridges or “teeth”, which they use to grind away at their surroundings to create tubular burrows. Are they extracting trace elements in the process and thus adding elements to the ocean soup?

The piddock stays in the burrow it digs for the entirety of its eight-year lifespan, with only its siphon exposed to take in water that it filters for food. When the piddock dies and leaves an empty tubular burrow, other marine life such as sea anemone, crabs and other molluscs may use the burrow.