Lost and found: how a single clue led to the rediscovery of a crab not seen in 225 years

Jfinding rare species thought to be extinct is never easy, but when Pierre A Mvogo Ndongo traveled to Sierra Leone in January 2021 in search of “lost” species of land crabs, the impression of searching for a needle in a haystack was particularly powerful due to the size of the “haystack”. For one of the species, the Afzelius crab (Afrithelphusa afzelii)Last seen in 1796, the only clue was the label on a specimen that simply read, “Sierra Leone.”

Mvogo Ndongo’s expedition was mainly in search of the rainbow-colored Sierra Leone crab. Afrithelphusa leonensis, lost to science for 65 years and considered possibly extinct – one of the species on Re:wild’s 25 “Most Wanted Lost Species” list. He also hoped – but did not expect – to find the crab of Afzelius (Afrithelphusa afzelii).

Both species are terrestrial crabs that live in burrows on the rainforest floor. “Most freshwater crabs in Africa live in rivers, streams and lakes,” says Mvogo Ndongo, senior lecturer at the Institute of Fisheries and Aquatic Sciences at the University of Douala in Cameroon.

“The species of interest belong to a unique Afrotropical family that includes members that can breathe air, which has allowed them to conquer darker habitats in the rainforest, often far from permanent water sources. . [They] are extremely colorful compared to their riparian cousins, and they can climb trees, live in rock crevices, burrow in marshes, or dig burrows in the forest floor,” he says.

Sierra Leone, Guinea and Liberia are the only countries in Africa where these crabs are present, and there are only five known species, he adds.

For three weeks, working alongside local communities in the northern, southern and southeastern provinces of Sierra Leone, Mvogo Ndongo found only false leads and frustration.

While many scientific discoveries (and rediscoveries) are aided by the rigorous and detailed notes of other scientists who have gone before, that was not the case here.

Afrithelphusa afzelii hadn’t been seen for 225 years and literally the only information on where to look for it was on the specimen’s label as ‘Sierra Leone’ – a very unspecific locality indeed,” says Mvogo Ndongo. “We deduced from this that it must have been collected within walking distance of Freetown, so we began our investigations in the forest nearby. But it was still too vague.

The team asked locals if they had seen crabs living in land away from rivers and streams until they encountered someone who could help them. “We were lucky – a man took us to his farm on the edge of the forest where, after intense research, the species was rediscovered,” he says.

The day after the Afzelius crab was found, Mvogo Ndongo traveled to the Sugarloaf forests, south of Freetown. With time running out due to an impending Covid-19 lockdown, he searched around Lake Guma, based on a local tip.

Deep in the forest, he finally found the Sierra Leone Crab. The crabs lived in burrows so deep that Mvogo Ndongo and his team had to carefully dig them out using pickaxes and machetes, before clearing the floor of the crabs to reveal the colorful crustaceans – the first live specimens seen since 1955.

Sierra Leone crab (Afrithelphusa leonensis)
Sierra Leone crab (Afrithelphusa leonensis), which is one of Re:wild’s top 25 species. Photography: Pierre A. Mvogo Ndongo/re:wild

Besides the rediscovered Sierra Leone crab and Afzelius crab, two new species of freshwater crabs have also been discovered. However, the crabs’ habitats are now threatened by the destruction of forest for agriculture and firewood.

“These discoveries are bittersweet because the joy of discovering lost species is mingled with the realization that, although they are not extinct, they are on the brink of extinction, and that urgent conservation interventions will be needed to protect these species in the long term”. says Neil Cumberlidge, a professor in the biology department at Northern Michigan University, who collaborated with Mvogo Ndongo on the expedition.

Now that scientists know the crabs are there, hopefully they can be protected.

“The new data generated by the expedition will allow us to reassess the red list status of each of these species which are likely to be ‘critically endangered’, i.e. close to extinction,” explains Cumberlidge. “The next step is to design a species action plan and implement on-the-ground protection measures with conservationists in Sierra Leone to save these species from extinction.”

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