Spirals in Time: The Secret Life and Curious Afterlife of Seashells (15 page)

The exact triggers for harmful algal blooms are still being studied but one important factor is well established: nutrients. Wherever nitrates and phosphates wash into seas and lakes it increases the chances of a harmful bloom forming because phytoplankton absorb those nutrients and grow, just like plants on land when fertiliser is added to the soil. The extra nutrients can very quickly kindle a lot more plankton.

The rise of artificial fertilisers and industrial-scale farming have played a big part in nutrient pollution. Since the industrial revolution, average phosphate levels in coastal waters have tripled, and nitrate levels have increased even further. Household cleaning products are also implicated. Environmentalists are campaigning for these nutrients to be banned, and in recent years the EU and US have set strict limits on phosphate levels in domestic laundry powders and dishwasher detergents (people living in hard-water areas will just have to make do with glassware that doesn’t gleam quite so brightly). The massive growth in fish farms in recent decades, especially for salmon, is also contributing to the flood of nutrients into the seas, from fish faeces and uneaten fish food.

As well as encouraging plankton blooms, the torrent of nutrients pouring into the ocean triggers a second ecological disaster. When the blooms come to an end, usually after several days, weeks or months, the dead plankton sink to the bottom where bacteria break them down. This uses up oxygen from the water and creates so-called dead zones where few aquatic species can survive. Since the 1960s, the number of dead zones worldwide has doubled every decade. One of the largest and most persistent is in the Gulf of Mexico, fringing the US states of Texas and Louisiana, which is caused largely by the polluted waters of the Mississippi River. In 2014 it covered 13,000 square kilometres (5,000 square miles), an area roughly the size of Connecticut or East Anglia. And as climate change warms up the oceans’ nutrient-rich soup, the extent and duration of harmful blooms and dead zones will only get worse.

Because of all these threats, many countries have introduced checks and balances to ensure shellfish is safe to eat. Early warning systems forecast and detect the onset of harmful algal blooms and, when they do strike, any nearby fisheries and fish farms will be closed until all risk of contamination has passed. Regular tests are carried out in many countries to check on levels of bacteria and toxins in shellfish. And while
raw sewage may not always be pumped into the sea as it was in days gone by, coastal pollution still remains an issue.

Across Europe, shellfish beds are assigned to strict classifications according to the levels of faecal coliform bacteria they contain. Grade A molluscs can be eaten straight from the sea (they have fewer than 230
E. coli
cells per 100g of flesh). Meanwhile Grade B molluscs, with higher coliform counts (up to 4,600
E. coli
per 100g), must be put through a process of purification (or depuration) before they’re eaten. Following the Emsworth oyster poisonings and various other typhoid outbreaks in Europe and the US, methods were developed for depurating bivalves. Now a well-established technique, it generally involves keeping live bivalves for 42 hours in tanks of fast-flowing clean water, often blitzed with UV light, to remove contaminants from their tissues. Some oysters are put through a depuration process even when they come from Grade A beds, just to make sure. There is also a Grade C (for shellfish with up to 60,000
E. coli
per 100g); these have to be moved to cleaner coastal waters before anyone is allowed to consider eating them. Molluscs with even higher coliform counts are strictly off limits.

Today, the majority of molluscs that make it to market – at least in developed countries – are fine to eat but only because we’ve had to invent ways of protecting ourselves from the pollutants we pour into the natural world. When it comes to eating molluscs, the other major issue is that some species are rather too delicious for their own good. A long time before we came up with ways of farming them, humans already had a terrible track record of taking too many molluscs from the sea.

Who ate all the clams?

The very earliest known case of any wild species being driven to the brink of extinction by people was a giant clam, around 125,000 years ago. Giant clams are the largest living seashells on the planet. They can grow to well over a metre (three feet)
in length, and live for longer than a century. I saw a living giant clam for the first time many years ago on Australia’s Great Barrier Reef and was amazed at just how huge it was. I smiled down at it and it seemed to grin back with its colourful, corrugated lips (their fleshy mantles acquire their bright colours from photosynthetic microbes called zooxanthellae living inside them, similar to those that live inside many corals). The clam sensed my shadow passing over it with hundreds of tiny eyes and hesitantly withdrew its mantle and closed its twinned shells. Their reputation as dangerous man-traps is utter nonsense with no record of anyone ever getting a part of themselves stuck inside one of these enormous bivalves. As with many legendary beasts, giant clams have far more to worry about from us than we do from them.

A few years ago, while exploring the warm clear waters of the Red Sea, a team of divers found a species of giant clam that no one had seen before. When he first caught sight of the deeply crimped shell,
Claudio Richter
from the Alfred Wegener Institute in Germany suspected this was something different to the seven known giant clam species. Further physical analysis and DNA tests confirmed the species was new to science and the team named it
Tridacna costata
(from the Latin word
costatus
, meaning ribbed). Scouring the reefs across the Gulf of Aqaba and the northern Red Sea, the divers found only a smattering of living
Tridacna costata
. To work out whether this has always been the case, the team also hunted for giant clams on land, in the sandy deserts fringing the Red Sea, in fossil reefs that flourished when sea levels were much higher. They saw that
Tridacna costata
was much more common 125,000 years ago, making up more than 80 per cent of the giant clams in the region. Today, they make up less than one per cent of the living clam community. Over the millennia these giant clams have also become distinctly less giant. They have shrunk in size to their present-day dimensions of 30 centimetres, or roughly a foot across. In the past, the clams would have weighed at least 20 times more than they do today.

The most likely explanation for the drastic decline in the clams’ stature and abundance is overfishing by humans. When people hunt, they almost always take the biggest animals first and a decline in average body size in a wild population is a good indication that humans have come along and helped themselves. In the case of the giant clams, those early people also left behind their fishing tools. In fossil reefs further along the Red Sea coast, in Eritrea, archaeologists have found palaeolithic stone tools that could have been oyster shuckers, left behind by people who waded out to gather clams and oysters. These gastronomical findings are reshaping our understanding of human migrations, providing new evidence that a coastal route out of Africa may have been important. And the loss of giant clams from the Red Sea, all those thousands of years ago, was just a taste of things to come.

The story of people overconsuming molluscs repeats itself again and again. Huge piles of empty shells show how abundant queen conch used to be across the Caribbean; now they are rare, and continue in their decline despite international efforts to protect them. In kelp forests of the Californian coast, divers have plunged further and further beneath the waves to find valuable abalone. The white and black species are now endangered, while the red and green are heading the same way. We are working our way into the depths and through the colours.

Perhaps the most famous mollusc stocks to collapse were the New York oysters that used to be pulled by the million from the Hudson River. Mark Kurlansky tells their story in
The Big Oyster,
of times when shellfish were eaten in Manhattan only a few blocks from where they grew. As stocks close to New York diminished, fisheries swept along the coast, leaving behind a trail of destruction. The same thing happened on America’s western seaboard and in Australia, where similar short-lived fisheries fed demand for oysters in San Francisco and Sydney.

Following all these declines, most of the molluscs we eat today are farmed, but there are a few places in the world where wild oysters still thrive. And it is there that people are trying very hard not to let history repeat itself.

Guardians of the oyster forest

A short way south along the coast from the baobab tree and its shell-island home, I came across more heaps of empty shells. I had crossed the wide mouth of the River Gambia on board a crowded and rusty ferry that crawled slower than walking pace towards Banjul. The Gambia’s capital sits on an island where the river meets the Atlantic Ocean. The rest of the country lies to the east, impossibly long and narrow, like a finger poking into Senegal. I continued my journey by taxi, crossing the bridge that links Banjul to the mainland, and by the side of the road I spied a series of silvery grey mounds and a queue of cars pulled over on the hard shoulder. This is where Gambians go to buy oysters.

In The Gambia, as elsewhere in the world, oysters are a delicacy. Gambian oysters also happen to be some of the cheapest you can buy. A bag of smoked oysters, scooped up in an empty tin can, will set you back 25 Gambian dalasis – less than 40 pence – and they come from an extraordinary place. Right on Banjul’s doorstep is a swathe of rich, green mangroves. The Tanbi Wetland National Park covers an area slightly smaller than the island of Manhattan. Living in small settlements scattered along the fringes of this aquatic forest are women who venture out and gather oysters from among the mangrove roots. Many of them are the sole breadwinners in their families; the men are either lazy or long gone. I was planning to meet the all-female oyster harvesters and the woman who has been helping them to help themselves while at the same time protecting The Gambia’s fragile wetlands.

Fatou Janha, known respectfully as Auntie Fatou, was born and raised in The Gambia but spent many years moving around the world with her diplomat husband; returning
home later in life, she decided one day to stop and talk to the oyster sellers.

Since she was a little girl, Fatou had seen women selling oysters by the roadside on the way into Banjul. ‘It suddenly occurred to me that these people need help,’ Fatou told me, as we sat in her office near the Old Jeshwang market with the voices of songbirds drifting in through the open windows. ‘But at first they didn’t understand why I should be interested in them. People have ignored them for a long time. As I always say, people buy oysters but they don’t look behind the oysters.’

On the day she stopped to talk to them, the oyster harvesters told Fatou about their lives and the troubles they faced making ends meet. She left her number and told them to call if there was any way she could help. She waited, and a few weeks later her phone rang.

When Fatou originally came back to The Gambia she set up a boutique, making and selling clothes. But for many years now, she has been pouring her energies into the TRY Oyster Women’s Association, the community project that grew from that first meeting and from Fatou’s vision that the women of Tanbi should be allowed to
try
to improve their lives.

Back in 2007 when TRY was founded, there was no denying that Tanbi’s natural resources were being pushed too far. Since the 1960s the local population has been growing, with people migrating in from neighbouring Senegal and Guinea-Bissau. Many of them are Jola, an ethnic group that has inhabited these coasts for centuries, in particular the troubled Casamance region of southern Senegal. For a long time they have been living and working in Tanbi. They have always supported themselves and their families by harvesting shellfish from these rich waters but, over the last decade or so, declining catches have forced them to roam deeper into the mangrove forests. The few shellfish they found were all rather scrawny and small. By the time Fatou came along, the oyster gatherers were finding it very difficult to make a living from the forest.

The simple but powerful thing Fatou did was to bring the oyster harvesters together and give them a unified voice. In the beginning, TRY had 40 members from one village. Fatou helped them to get a bank account, raised some funds and set up a micro-finance scheme so the women could start other small businesses and make money during the closed rainy season. She organised classes to teach the women and their daughters to bake and make handicrafts, provided healthcare advice, and encouraged them to start saving for the first time; in particular, she wanted the women to be able to afford school fees and allow their daughters to finish their education. Word soon spread, and now TRY has more than 500 members from 15 villages across Tanbi. Women who a few years previously were strangers have now became close friends and co-workers.

Fatou suggested we pay a visit to the mangroves to see some of the women at work, so we rented a small boat and slowly motored along the tributaries, known as
bolongs
, that percolate through the Tanbi wetlands and divide the forest into a mosaic of islands. Salt-encrusted leaves of mangrove trees rose up around us with their stilt roots looping and dipping into the water. A Malachite Kingfisher flashed past, a dart of electric blue, and a gaggle of pelicans rested in high branches, preening their feathers with enormous beaks. Around 360 bird species are known to inhabit the wetlands, including many global migrants, and birdwatchers fly in from across the world to see them. There are other forest denizens that I didn’t see, but it was good to know that Red Colobus monkeys were perched somewhere in the dense thickets, there were short-clawed otters padding through the undergrowth in search of crabs, and perhaps even a manatee was hiding submerged somewhere nearby in the murky waters.