Spirals in Time: The Secret Life and Curious Afterlife of Seashells (40 page)

Using this suite of meticulous methods, the collectors are probing deeper than ever into the world of molluscs. In particular, they are uncovering an incalculable trove of micro-molluscs. These weeny animals are truly the secret gems of the sea. They come in a riot of exquisite colours, like a jar of jellybeans, with neon spots and stripes, yellow, purple, green and red. There are tiny clams with a sweep of pink tentacles sticking out, snails with glassy, transparent shells and kaleidoscopic mantles that show through from underneath, and bivalves that unfurl their colourful mantles over their shells and crawl about on their feet as if they were gastropods. Almost nothing is known about these animals. We don’t know what they eat, what eats them, what strange and useful molecules they might contain or where exactly
they belong on the sprawling tree of molluscan life. There are so few experts who specialise in these minute species that many of the samples Bouchet and the team collect could remain for years on a museum shelf, found and logged but not fully identified. Taxonomists call these neglected species ‘orphans’. Even greater mysteries remain to be unravelled, hidden in oceanic nooks where molluscs reside but no one has yet worked out how to get hold of them.

Divers from Bouchet’s team went gathering molluscs along a vertical wall of coral that plunges into the Bismarck Sea off Nago, 1,000 metres beneath the waves. The wall is pockmarked with caves, inside which the divers found a tantalising array of previously unknown shells, all of them between one and five millimetres in size, and all of them empty and dead. No matter how hard they tried and how carefully they looked, they couldn’t find a single living mollusc responsible for making these enigmatic shells. The animals probably live deep within the cracks of this towering wall. The only reason we know they exist at all is because their shells drop down into the hands of the diving scientists. And we can only imagine what else lives in there, out of reach and out of sight.

There are undoubtedly many molluscs that will only be found by teams of experts with finely tuned searching skills and specialist equipment, but you don’t need scuba gear or microscopes or deep-diving submersible vehicles to have your own encounters with a host of curious shelled creatures. Next time you visit a beach or swim in the sea or even take a stroll somewhere a long way from the ocean, look out for the shells that are all around you. Then you can read the stories written into shells, the clues left here and there that tell you about the shell-maker’s life.

How big was your shell when it was a baby? Follow the spirals of a gastropod inwards towards its middle; the innermost whorls, the smoothest part often with an obvious line around the edge; this is the shell that the young snail
wore when it first hatched. In some bivalves you can also spy a smooth inner part, right next to the hinge where the two halves of their shell fit together.

Which way does your shell coil? Hold it, tip pointing down, and see if you have a common right-coiler or perhaps it’s a rare sinistral specimen, one that may have found life difficult and sex an awkward, mismatched challenge.

The shape of your shell, its ornaments, crenulations, striations and spines, will tell you about its life; perhaps it is a flattened clam that lay on the seabed, or a screw-shaped gastropod that dug its way down. Or is it covered in prongs to lodge itself in the sand, to try to stop it from being swept away?

Take a close look at patterns drawn across shells, those notes-to-self written so they didn’t forget where they were in their shell-making efforts. Is there a point where the regular pattern goes awry? Did your shell get broken or attacked? Did it survive and keep on growing, eventually getting back in line and continuing with its elegant, decorated spiral?

Did your mollusc pick up any hitch-hikers, while it was alive or after it vacated its shell? You might spot barnacles or bryozoans (both formerly thought to be molluscs), or hydroids like tiny fir trees, or worms living inside white, spiralling tubes.

You might find gastropod shells with an elongated notch where a long siphon stuck out, probing and tasting the water in search of prey. These were the hunters, and you will also find their victims. Shells with neat holes drilled in them are testament to the evolution of so many molluscan ways of hunting and dining, and the fact that they’re not shy of eating each other. Some shells might have a ring etched in them but not quite a hole, the sign of an interrupted assault.

Once you’ve read these stories, you can either leave the shells behind or take a few home as a reminder of a day at
the beach or a walk in the woods. And maybe you’ll be lucky enough to come face to face with shells that still have living occupants. Down at low tide you might spot dog whelks laying eggs like swollen grains of rice on the underside of boulders. In a rock pool you might catch a starfish attacking a limpet and getting its tube feet stamped on, or a pair of hermit crabs fighting over their shells. Perhaps, in shallow water, you’ll spy a scallop swimming past like a living castanet, a cockleshell hopping across the seabed or a razor clam swiftly and efficiently digging its way out of sight. And maybe you’ll find a sea snail, or a pond or land snail, and let it creep along your finger for a moment, watch it glide along its silvery trail with minute waves of its singular foot, before putting it carefully back where you found it.

A Note on Shell-collecting

I
f you buy a shell, especially a nice, shiny specimen, you should know that it wasn’t picked up already empty and abandoned on a beach. Plenty of shells are left behind by molluscs that died of disease, predation, old age or some other fate, but those ones don’t stay pristine for long. They get bashed about by waves and colonised by other living, encrusting, boring things, and soon they lose their gloss and are in no fit state for sale. Chances are that your gleaming shell was taken from a living animal; it was collected and killed and its shell removed and sold into the shell trade, so ultimately you could buy it.

Killing animals for human use is nothing new, of course, especially molluscs. The problem is that compared to the molluscs we eat, much less is known about ornamental species; large, beautiful shells taken from tropical coral reefs, small decorative gems and other shells used for their mother-of-pearl are all traded in huge quantities around the world. Exactly how many shells are traded each year is unclear because data are not always available or complete. It’s thought around 5,000 mollusc species are targeted for their shells, but there’s very little information about the impact of that harvest. However, anecdotal reports from shell collectors and sellers suggest that in many countries the trade is affecting wild populations. In Kenya, Tanzania, India and the Philippines many mollusc species have shells that are smaller than they used to be, a strong indication that all is not well and the larger specimens have been depleted. Local supplies have commonly run low, and traders have been forced to import shells from elsewhere; if you buy a shell on holiday in Hawaii or Florida, it most probably came from Mexico or Asia.

Despite all this, it is unlikely that a marine mollusc species will ever go extinct just because of collecting for the shell
trade, except possibly for a few unlucky species with very small ranges. There have, however, been local extinctions. Giant clams and tritons have been wiped out from parts of the Indo-Pacific. In the Western Visayas of the Philippines Windowpane Oysters were virtually eradicated when mechanical dredges and rakes were used to scrape them up from the seabed; now the Windowpane Oyster industry in the Philippines, which crafts the shells into ornaments, relies on imports from Indonesia.

On the whole, the ornamental shell trade is less of a conservation concern than the sprawling global commerce in other marine species, such as the trade in shark fins to make into soup, or seahorses for traditional Asian medicines. Nevertheless, collecting shells can and does leave its mark on the natural world.

The inevitability that shells will become increasingly rare was the assumption behind a 1980s enterprise called Rare Shell Investment Services. ‘There is little that can go wrong when investing in a disappearing, rare commodity’ was the company’s appalling claim. They encouraged investors to sink their cash into mollusc species that they reckoned would become very difficult to find but collectors would still want to own. Rare Shell Investment Services doesn’t seem to be operating today, but there are signs that some shell prices have risen, while others fell when more specimens showed up, as happened with the Glory of the Sea.

However, if you care more about protecting wild species than plundering them for a profit, it’s very difficult to know what to buy. The trade in ornamental shells tends to be poorly regulated and managed compared to the trade in edible species. Some countries have legislation protecting certain vulnerable species, although those laws aren’t always well enforced. There are no major aquaculture efforts underway to farm ornamental molluscs besides giant clams (which are mainly for the aquarium trade and to re-stock coral reefs). International trade in all the giant clam species is
strictly regulated by CITES (the Convention on International Trade in Endangered Species of Wild Fauna and Flora), so technically their harvest and sale shouldn’t damage wild populations. If you do want to buy a giant clam, dead or alive, shell or living animal, you should make sure it’s been traded with all the necessary permits.

Nautiluses and any other big shells should definitely be avoided (in general the bigger an animal, the longer it lives, the slower it grows and the more vulnerable it is to being over-hunted, which is certainly the case for nautiluses). On the whole it’s impossible to know where a shell came from and how it was caught; there are no eco-labels for ornamental shells certifying that they come from sustainable sources. Unless you care a whole lot about having commercially bought shells in your life, it’s perhaps best to resist temptation and leave them all alone.

As for finding your own seashells on beaches, here things are much more in your control. Always stick to local regulations and ask around; there might be a limit on the daily number and minimum size of shells that can be collected, you might need a permit to gather particular species and collecting is often prohibited in protected areas or nature reserves.

It’s also up to you to make as little impact on the environment as possible while you’re shell-collecting, although most of this is common sense: carefully turn rocks back over after you’ve peered underneath; don’t trample across delicate habitats; don’t take every single specimen you find, and remember that it makes ecological sense not to take any living molluscs.

And for your own sake, watch out for the cone snails.

Glossary

A Word in your Shell-like

Aculifera
A proposed grouping of molluscs including all the animals without single shells; includes the chitons, solenogastres and caudofoveates.

Ammonite
A group of extinct cephalopods, mostly with coiled shells, that lived during the Triassic, Jurassic and Cretaceous periods. They form part of the ammonoid lineage that first evolved in the Devonian. Their fossils were often known as snakestones.

Anthropogenic
Caused or produced by humans, e.g. anthropogenic climate change.

Aragonite
A form of calcium carbonate that is about 1.5 times more soluble than calcite. Most adult mollusc shells are made of aragonite. Some are calcite. Some are a bit of both.

Belemnite
An extinct group of cephalopods with internal, bullet-shaped shells. Their fossils have often been called thunderstones.

Benthic
Anything belonging to the seabed.

Bivalve
The class of molluscs with shells in two parts (often more or less equal in size) including clams, mussels, cockles and scallops.

Byssus
A term used since the fifteenth century for the strong, stretchy protein fibres with a sticky pad at one end that bivalves secrete from their feet to fix to rocks or to the seabed. Cleaned, carded and spun, they can form golden threads known as sea-silk.

Calcite
A form of calcium carbonate that is more stable than aragonite.

Calcium carbonate
A white solid made from calcium, carbon and oxygen (CaCO
3
). It is the main building material of molluscan shells, and comes in two main forms: calcite and aragonite.

Caudofoveate
Molluscs, but not as you know them. An obscure class of worm-like, shell-free animals that live in soft sediments. Also known as Chaetodermomorpha.

Cephalopod
The class of molluscs including octopuses, squid, cuttlefishes, argonauts and chambered nautiluses. Most of them have lost or reduced their shells.

Chiton
The class of molluscs that have eight shell plates lined up across their backs. They generally live clamped tightly to rocks and can roll up in a ball in defence. Pronounced ‘kai-ton’.

Coleoid
The mollusc lineage containing mostly soft-bodied cephalopods, including octopuses, squid, cuttlefishes and the extinct belemnites. They first emerged in the Devonian, around 400 million years ago.