Let’s talk about shells

What’s your favourite shell?

I have a real soft spot for cowries. There are lots of species found around the world, and I love finding the tiny European ones on beaches near my home in France. There’s one particular secret spot where I know I can always find one or two. They’re about the size of a little fingernail, so they take some hunting for!

I’ve also found much bigger cowries in tropical seas. Their shells feel like they’re made of polished porcelain, because a soft tissue called the ‘mantle’ flaps over them, keeping them smooth and shiny.

What shells can we expect to find around the UK?

There are various types of shells in different habitats around the UK's coast.

On sandy beaches you’ll usually find lots of bivalve shells — ones that come in two parts, often fan-shaped and crinkled, like clams and cockles. Bivalves tend to dig down in the sand and use a long tube, like a snorkel, to breathe water and feed on tiny floating particles. Next time you’re walking across a sandy beach, think about the living bivalves hidden beneath your feet.

All sorts of spiralling snail shells are common on rocky shores, things like periwinkles, dog whelks and top shells. They're all types of snails, otherwise known as gastropods. Limpets are sea snails too, although their shells untwist as they grow, and they look more like little volcanoes clamped to rocks at low tide.

You can also find other types of shells washed up on beaches from animals that live further offshore, like flat white cuttlebones, which are the internal shells of cuttlefish.

Has climate change impacted shells in any way?

The ocean absorbs huge amounts of carbon dioxide from the atmosphere. This means our ocean has become around 30% more acidic than before the industrial revolution, and it’s expected to get much worse in the years ahead.

Ocean acidification is a major threat to marine animals, especially those that make shells from calcium carbonate, the same mineral as chalk. By altering the chemical balance of the ocean, this drop in pH is making it harder for many molluscs to obtain enough carbonate ions from the water to make their shells.

Most threatened are the tiny swimming sea snails, known as pteropods or sea butterflies, which make very thin, delicate shells. They’re important food for many other marine animals - from fish to birds and whales, so the loss of sea butterflies from the ocean would have major knock-on effects throughout ecosystems for biodiversity.

How does fishing impact shells and the creatures that live in them?

Shells form the basis of a bunch of important habitats, including oyster reefs and mussel beds. Scotland has some stunning reefs made of flame shells (they have fiery orange tentacles), which are home to a rich array of species, including crabs and brittlestars.

These sorts of habitats and species have been historically targeted by fisheries using highly destructive gears, with scallop and oyster dredges dragged over the seabed causing some of the worst ecological damage.

UK oyster reefs have been almost entirely wiped out by fishing over the last century or so, but thankfully, efforts are now underway to reintroduce native oysters around the UK coast and rebuild their important, biodiverse ecosystems.

Are there any other threats of human activity?

New threats are on the horizon for shell-making species, too. Miles below in the deep sea, on scorching hot hydrothermal vents, there are amazing species like scaly foot snails and giant vent clams that would be destroyed and lose their habitat if deep-sea mining begins.

Mining companies want to start extracting metals from inside the tall, rocky vent chimneys, but many mollusc species live nowhere else on the planet except for in these vents. Because of this rising threat, almost 200 species were recently added to the IUCN’s Red List of endangered species. Scientists, governments, civil society, and corporations are also calling for a moratorium on deep-sea mining, so we can fully understand what the environmental impacts will be before this new industry is allowed to start.

Dr. Helen Scales is a marine biologist, writer, and documentary maker focusing on connections between people, science, and the living world. Her book, What A Shell Can Tell, depicts over 50 kinds of shells and molluscs from around the world, through interactive questions and captivating illustrations. For nature enthusiasts and future biologists aged 6-9, What a Shell Can Tell is also a vehicle to open a wider conversation about the world around us. The book is available now.