Rare crab species rediscovered in Ebo Forest after more than a century

Cameroon’s Ebo Forest is a special place. With its lush tree canopies, mountains and river valleys stretched out over 2,000 square kilometers, it is truly a paradise for both the natural and scientific worlds. As the surrounding areas of southwest Cameroon continue to face threats from logging concessions and other destructive projects, the forest (while still intact) also plays a critical role of providing refuge for its rich and diverse pool of inhabitants – including the only troop of chimpanzees in the world to use tools to both crack nuts and fish for termites.

Among the animals and plants most threatened by human activities in the area are a variety of freshwater crabs, which mainly dwell in Ebo Forest’s rivers and streams. Southwest Cameroon is home to 22 different crab species, nine of which are endemic. One of these is Louisea yabassi, a small, semi-terrestrial, uniformly light brown and rusty colored crab that is extremely rare, having fallen off the radar since the first specimens were seen and collected in 1908.

“That’s what makes the species so special,” says Dr. Pierre A. Mvogo Ndongo, a carcinologist and lecturer at the University of Douala in Cameroon.

He and his colleagues at Northern Michigan University in the United States, and at the Humboldt Natural History Museum in Berlin, realized that those 1908 specimens of L. yabassi had been previously misidentified and were likely to be a different species altogether. Unfortunately, the poor condition of the specimens meant that extracting DNA from them to shed light on their evolutionary history proved all but impossible.

First sighting for over 110 years

But Mvogo Ndongo and his team were undeterred. The specimens collected in the Ebo forest undoubtedly belonged to the genus Louisea, but it was far less certain that they belonged to any of the known species. In 2019 and 2020, Mvogo Ndongo and his team ventured out into the tropical oasis of Ebo on two separate field surveys to search for L. yabassi in the hopes that they could confirm the species’ continued existence, as well as collect and identify other types of freshwater crustaceans along the way.

Both trips turned out to be a success: 20 individuals were found in and around two streams flowing into the Dibamba River in Cameroon’s Littoral region in the 2019 survey, and a further 15 from one of these streams in 2020.

“It was fantastic – it felt very good to rediscover the specimens of Louisea yabassi and to be the first scientist to see this species for well over 110 years,” says Mvogo Ndongo, who also rediscovered the Sierra Leone Crab, one of Re:wild’s most wanted lost species. “Honestly, we thought that L. yabassi might well be extinct.”

With these two populations, the team could finally compare the physical characteristics of the new individuals with the original ones, and the DNA with that of other crabs in the same genus, to verify they had indeed come across L. yabassi. What the rediscovery also revealed, however, was that this species was already in danger.

A concerning future

In the region they surveyed, the team reported that much of the natural vegetation had been destroyed by logging, agriculture and pesticides. These activities will directly impact L. yabassi by disturbing and fragmenting its habitat and, given that the rediscovered populations were so small, “I became concerned about the long-term survival of this species,” says Mvogo Ndongo.

L. yabassi is an important player within the freshwater community of Ebo Forest. Ecologically, it is part of a complex food web that includes the Nigeria-Cameroon Chimpanzee, the Western Gorilla, Goliath Frog, Forest Elephant, Preuss's Red Colobus Monkey, Drill, and African Grey Parrot. The rivers and streams where the rare crabs are found also act as spawning grounds for several other invertebrates and fish, and provide a safe haven for many of the forest’s other charismatic aquatic animals such as crocodiles, pythons, and swamp otters.

Because these crabs sometimes venture onto land (Mvogo Ndongo collected some individuals from under fallen leaves and in burrows near the streams), it’s possible they may also scavenge animal and plant matter on the forest floor, similarly to other species of African freshwater crabs.

All this makes a carefully designed conservation plan to protect the species from extinction a necessity, according to scientists.

“A more complete picture of the biology of this species and the threats that it is facing can then be used to educate and enable local people to adopt practices that are less damaging to the forest ecosystem, and to the crab’s most sensitive habitat,” explains Mvogo Ndongo.

One of his next projects will be to do exactly this, studying the population levels, ecology, habitat requirements and dangers for several threatened species of freshwater crabs in Cameroon, including L. yabassi, to figure out how best to shield them from the harm that is increasingly encroaching on the country’s wildlife reserves.

Crucially, the consequences of L. yabassi’s rediscovery serve as a reminder of the globally unique habitats that Ebo Forest provides – and the tragedy of losing even one of its hundreds of special species.