RÍO LAGARTOS, MEXICO — It is not a glamorous creature.

The sea cucumber, a relative of the starfish and sea urchin, isn’t much more than a blob creeping across the ocean floor on tentacle-feet, munching on algae and plankton. The most interesting thing about the animal may be that some species defend themselves by ejecting respiratory tissues through the anus in the direction of the attacker.

But here on the Yucatán Peninsula, the uncharismatic sea cucumber has become so sought-after that the local populations of two species — Isostichopus badionotus and Holothuria floridana — have collapsed.

In the two-week fishing season last April, divers in this town hauled in 14 tonnes of sea cucumber — a sharp drop from the 260 tonnes harvested four years ago.

The decline is largely the result of overfishing driven by high demand in Asia, where dried sea cucumbers are eaten as a delicacy and can sell for more than $300 a pound. Sea cucumbers are said to deter muscle aging, boost the immune system, and treat fatigue and arthritis.

At least 16 species of sea cucumber worldwide are now threatened with extinction because of intense harvesting, according to the International Union for Conservation of Nature. Another seven are endangered, and nine are vulnerable.

Researchers say reduced numbers of sea cucumbers may lead to decreased nutrient recycling and biodiversity on the seafloor, and may interrupt the food chain.

But while sea cucumber fisheries throughout the world have long been troubled, the Yucatán offers one of the most vivid examples of the challenges facing the animal.

“This creature went from being just a worm on the seafloor that these divers totally ignored to being something that they called ‘black gold’ within the span of a couple of years,” said Abigail Bennett, an assistant professor of fisheries and wildlife at Michigan State University and co-author of an article about the sea cucumber trade in the journal World Development.

She and others trace sea cucumber exploitation in the Yucatán to around 2012, when hundreds of fishermen realized the value of the catch in Asia. With air compressors made from 6-horsepower motors and beer kegs, divers began scouring the ocean floor for sea cucumbers.

The divers used the sudden income to pay off debts, build new houses and fix up boats. But to keep the money flowing, they also took bigger risks. At least 40 divers from coastal communities in the Yucatán have died after ascending to the surface too quickly or staying on the seafloor too long while harvesting sea cucumbers.

Hundreds of others have been treated for decompression sickness — “the bends” — and other injuries related to the sea cucumber harvest.

“I attended to one and then another and another,” said Dr. Juan Tec, who works at the public hospital in Tizimín.

Some days, he recalled, patients sprawled on the floor as they waited for their turn in a three-bed hyperbaric chamber. Others were rushed in immediately for life-threatening injuries.

“You lose track of time,” said Angel Gamboa, a diving fisherman who suffered spinal cord decompression after spending about three hours gathering sea cucumbers off the Yucatán coast. “This never passed through my mind.”

But even as the fishing frenzy was proving hazardous to divers, it was becoming equally threatening to the resource itself.

In recent years, government regulations limited the sea cucumber harvesting period to 14 days, setting catch quotas at 250 kilograms per fishing boat.

With limited oversight and enforcement, though, populations were given no time to grow and reproduce, leading to their near-total decline within just five years of authorized fishing.

“We could see that it was happening because of the fishing behaviour, but we couldn’t completely stop it,” said Alicia Poot-Salazar, an investigator who recommends catch quotas to Mexico’s National Commission on Aquaculture and Fisheries. “It developed so fast you couldn’t control everything.”

In retrospect, monitoring and enforcement systems should have been better, she said. The commission also issued too few harvesting permits, leaving unlicensed fishing crews with little incentive to follow the rules and limit catches.

In April, Salazar said 594 boats were issued permits to collect sea cucumbers — among a population of roughly 10,000 Yucatán fishermen.

Others suggested that local fishing co-operatives themselves should be given a greater role in policies aimed at improving governance of the resource.

To some experts, though, the lowly sea cucumber provides yet another example of the frequent obstacles to sustainable harvesting.

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“It’s exemplary of the ways we kind of outrun ourselves and are left with a tragic situation,” said Michael Schoon, an associate professor of sustainability at Arizona State University.

Often, these loops are thought about in the context of enormous trends, such as climate change, he said. But the plight of the sea cucumber shows that even seemingly insignificant shifts can have a profound effect.

In the town of Río Lagartos, there were hardly any sea cucumbers left to collect this year. According to Tec, no divers were killed, either.

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