The sun had barely risen over the Pacific Ocean when a small motorboat carrying a team of Indigenous artisans and Mexican biologists dropped anchor in a rocky cove near Bahías de Huatulco.
Mauro Habacuc Avendaño Luis, one of the craftsmen, was the first to wade to shore. With an agility belying his age, he struck out over the boulders exposed by low tide. Crouching on a slippery ledge pounded by surf, he reached inside a crevice between two rocks. There, lodged among the urchins, was a snail with a knobby gray shell the size of a walnut. The sight might not dazzle tourists who travel here to see humpback whales, but for Mr. Avendaño, 85, these drab little mollusks represent a way of life.
Marine snails in the genus Plicopurpura are sacred to the Mixtec people of Pinotepa de Don Luis, a small town in southwestern Oaxaca. Men like Mr. Avendaño have been sustainably “milking” them for radiant purple dye for at least 1,500 years. The color suffuses Mixtec textiles and spiritual beliefs. Called tixinda, it symbolizes fertility and death, as well as mythic ties between lunar cycles, women and the sea.
The future of these traditions — and the fate of the snails — are uncertain. The mollusks are subject to intense poaching pressure despite federal protections intended to protect them. Fishermen break them (and the other mollusks they eat) open and sell the meat to local restaurants. Tourists who comb the beaches pluck snails off the rocks and toss them aside.
A severe earthquake in 2020 thrust formerly submerged parts of their habitat above sea level, fatally tossing other mollusks in the snail’s food web to the air, and making once inaccessible places more available to poachers.
Decades ago, dense clusters of snails the size of doorknobs were easy to find, according to Mr. Avendaño. “Full of snails,” he said, sweeping a calloused, violet-stained hand across the coves. Now, most of the snails he finds are small, just over an inch, and yield only a few milliliters of dye.
The snail populations crashed during the 1980s, when a Japanese textile company hired local fishermen to dye bolts of kimono silk. The Mixtecs collect dye a few months a year (not during the summer when the snails are breeding) and return the snails to the rocks, holding them in place until they reattach. But the fishermen extracted dye year-round and left the snails to bake in the sun or chucked them into open water.
“The snails don’t wash back up and then attach,” said Marta Turok, an anthropologist and expert in Mexican craft traditions. “They sink down and die.”
Generations of Mixtec women have woven the amethyst thread into elaborate wrap skirts in which they are married and, ultimately, buried. When Ms. Turok learned these textiles were on track to disappear with the snails, she connected the tintoreros (as the dyers are known in Spanish) to biologists who could collect data proving the mollusks were in steep decline.
“My work, and that of my colleagues, was to demonstrate scientifically that the tintoreros were right,” said Javier Acevedo García, one of those biologists. He found that the devastation — especially the disappearance of the largest snails that were about 40 years old — was accurate. Without interference from fishermen, it would take roughly 20 years for these populations to rebound to their former levels, according to his research.
Getting the authorities to act wasn’t easy, according to Ms. Turok, who worked for the government at the time. “Environment was not on the agenda,” she said. After years of campaigning, the tintoreros and their allies succeeded in securing federal protections for the snails known scientifically as Plicopurpura pansa in 1988.
But now it seems as though the species that the group labored to save may not be a species at all. Scientific studies have since suggested that the dye-producing snails might be members of P. columellaris, a different, unprotected species found in the same coastal habitats. The editors of the World Register of Marine Species, an online database maintained by an international group of specialists, have determined that the name Plicopurpura pansa is invalid.
The Mixtecs see two distinct groups of snails. The mollusks they use secrete more dye, and their shells aren’t as thick. Biologists have observed variations in the snails’ internal anatomy as well, such as the number and placement of microscopic teeth on the radula, a long, ribbonlike feeding organ the snails use like cheese graters to penetrate the shells of other mollusks.
Physical diversity, however, doesn’t always signal species-level divides.
“People repeatedly ‘discover’ snails in this group and give them names,” said Martine Claremont, who wrote her dissertation on Rapaninae, the subfamily to which the Oaxacan snails belong. Over the past couple centuries, she explained, gung-ho scientists have christened new species based on distinctive individuals, leading to multiple overlapping names.
When scientists identify redundancies, the earliest name — in this case P. columellaris — takes precedent.
At first glance, these classifications might seem like biological inside baseball. What difference does a bit of Latin nomenclature make? Changes to scientific names can have consequences for animals and the conservationists who defend them.
“The law is protecting a species that is not recognized by the scientific community,” said Sonia Hernandez, a biologist at Olive-Harvey College in Chicago. “Therefore, somebody could potentially harvest the mollusk and not be punished by any enforcement. They wouldn’t be breaking any law.”
Although Dr. Hernandez and other scientists say more research is necessary to clarify the relationship between the snails, they worry the uncertainty could create loopholes for a company to harvest the remaining snails — and that an ancient Mixtec tradition could vanish with them.
Cultures throughout Central America once collected dye from the snails, but now, in a world of cheap synthetic pigments, Mr. Avendaño and his family are among the few people keeping the practice alive. To collect the dye, they detach the mollusks from the rocks and press their rubbery feet until a creamy fluid wells up inside their shells. Then, they tip the liquid onto skeins of cotton yarn wrapped around their wrists. Exposed to air and sunlight, the fibers transform. Lichen yellow becomes peacock green and, finally, brilliant shades of purple.
Dyeing the thread is dangerous work. “We sometimes risk our lives to be able to bring that color home,” Mr. Avendaño’s son, Rafael Avendaño Lopez, said. The Avendaños have lost relatives who slipped on the rocks and drowned in the unpredictable surf. Preserving ancestral traditions, they say, is worth the danger.
In December, the Mixtec dyers, or tintoreros, and scientists invited Dr. Hernandez and Oscar Pineda-Catalan, a conservation biologist at the University of Chicago, to perform an anatomical and genetic analysis to answer the species question once and for all. The husband and wife team say previous studies have not been detailed enough to be conclusive.
“It’s really important that a comprehensive, rigorous description of the species incorporate both morphological and molecular data,” Dr. Pineda-Catalan said. He noted that previous researchers have based their conclusions on just one or the other. “We need a little bit more information,” he said.
When Drs. Hernandez and Pineda-Catalan ran the experiment, they set up a makeshift laboratory in a rural Airbnb near Bahías de Huatulco to give their Mixtec collaborators access. The biologists said they wanted to avoid the long history of researchers swooping in, taking samples and whisking them away to inaccessible facilities.
“The traditional laboratory is people wearing lab coats, and the nonscientists are outside, and the scientists are inside, and they are the only ones who possess the knowledge and skills,” Dr. Hernandez said. This system has tended to exclude Native communities.
“It was important to be there,” the younger Mr. Avendaño said.
“We know everything about the field. No one can teach us what we already know there,” he said. “That’s ancestral knowledge passed down by our forebears. But in scientific and biological terms, we don’t have that knowledge or the tools to determine what type of blood or DNA it has.”
The conditions in the rustic cabana required the scientists to improvise. The lights in the cabana were dim, the space was hardly sterile and the presence of other invertebrates threatened to ruin the samples. “We found a scorpion in our sheets last night,” Dr. Hernandez said as she sat down at a dissection microscope poised on a rickety table in the kitchen turned laboratory. Still, they were able to successfully run the experiment.
After measuring, photographing and dissecting snails, the scientists took biopsies, and extracted and purified the DNA. They then ran a polymerase chain reaction, a process sometimes called molecular photocopying, which generates millions of copies of relevant genes. With enough copies, scientists can sequence and compare the DNA of different specimens. The more similar two sequences are, the more likely it is that the specimens belong to the same species.
The scientists and tintoreros, who sent the DNA to the National Institute of Genomic Medicine in Mexico City for processing, are now waiting for the sequences.
Rafael Avendaño Lopez said he wasn’t nervous about the results. No matter what species the snails are, he said, “we’ll continue fighting to protect them.”
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