When Manuel Lopes-Lima set out to survey aquatic biodiversity on the Corubal River in 2022, he’d set his expectations very low. The river that straddles the West African nations of Guinea and Guinea-Bissau was, after all, very remote and grossly understudied.
Two expeditions later, the story has turned on its heels.
With the help of environmental DNA sampling and analysis, Lopes-Lima and his team identified 125 species of aquatic and terrestrial vertebrates in the Corubal. This includes critically endangered western chimpanzees (Pan troglodytes verus) and freshwater mussels (Pleiodon ovatus) as well as 21 other species, mostly fish, that weren’t known to exist in Guinea-Bissau.
“We were not expecting the huge diversity that we found,” Manuel Lopes-Lima, group lead at the Research Centre in Biodiversity and Genetic Resources at the University of Porto in Portugal, told Mongabay in a video interview. “We were expecting a lot less.”
In a study= published in the journal Bioscience, the team laid out the methodology they used to filter DNA from water samples collected from the Corubal. According to the study, the findings emphasize the “conservation importance of the Corubal, provide a baseline for future monitoring, and highlight the challenges and opportunities of eDNA surveys in remote tropical rivers.”
“Corubal is one of the last free rivers in Africa,” Lopes-Lima said. “There’s no major big city along the river and no dams, and that makes this river particularly interesting in terms of conservation needs.”
Flowing nearly 560 kilometers (350 miles), the Corubal rises from the highlands of Guinea, forms a section of the border with Guinea-Bissau, then meanders through the latter country before emptying out into the Atlantic Ocean. Along the way, it serves as a source of freshwater for animals living in the river basin. Large-scale studies to monitor biodiversity in the river haven’t been undertaken in recent years. However, smaller expeditions in the past have found the river and its basin to be home to a wide gamut of species, including Senegal flapshell turtles (Cyclanorbis senegalensis), African manatees (Trichechus senegalensis), Nile crocodiles (Crocodylus niloticus) and hippos (Hippopotamus amphibius).
When Lopes-Lima and his team decided to study the Corubal River, environmental DNA analysis seemed like the best way to understand the biodiversity that lives there. Previously, Lopes-Lima used to dive or go snorkeling to study and monitor aquatic species. But this came with challenges. “Especially working in tropical rivers in remote areas, it’s sometimes dangerous,” he said. “There’s a lot of parasites which might be vectors of diseases, and also dangerous animals like crocodiles and hippos.”
Environmental DNA (eDNA) has found increasing popularity as a noninvasive method of conducting biodiversity surveys over large areas. It requires collecting and detecting DNA left behind by animals in water, air and soil via their hair, fur and saliva, among other things. Recent studies have also explored swabbing leaves in forests to gather DNA samples of terrestrial animals.
Lopes-Lima and his team undertook two expeditions, one in 2022 and one in 2023, to collect samples from the part of the river that flows through Guinea-Bissau. Traveling in narrow canoes, the team collected water samples from 25 points along the river. From these, they extracted DNA to identify the species associated with them.
The recently published study covers only the findings from the expedition in 2022. This includes species that had previously not been recorded in the country, such as the Egyptian fruit bat (Rousettus aegyptiacus) and the gray-throated rail (Canirallus oculeus). “It was interesting to see that we could understand the biodiversity of the river itself, but also the animals that use the river to drink water or as a refuge in the dry season,” Lopes-Lima said.
The team also simultaneously worked on building a reference database for species in the region. For this purpose, they were accompanied by a team of scientists who collected specimens and tissues from animals in order to build a database, especially for insects, mollusks and smaller mammals that haven’t been well-represented in DNA reference databases. “The problem is that many of the species in Guinea-Bissau were never sequenced,” Lopes-Lima said. “Because they are so remote and difficult to study, we didn’t have references for many of them.”
While the team analyzes the samples from the 2023 expedition, it’s also planning a third trip that would potentially cover the upstream part of the river that lies in Guinea. The ability to gather and process so much biodiversity data from a remote tropical river has also encouraged the researchers to cast a wider net across the continent. Lopes-Lima said he’s also currently working to train scientists, develop eDNA protocol, and build capacity to conduct rapid biodiversity assessment surveys in rivers in Namibia and other parts of Southern Africa.
“We are trying to standardize and optimize these methods to maximize the biodiversity you get while minimizing the cost,” he said. “Not only to see the biodiversity trends, but to use it for monitoring and see if conservation actions are helping or not.”
Citation:
Lopes-Lima, M., Prié, V., Camará, M., Ceríaco, L. M., Fernandes, V., Ferreira, S., … Beja, P. (2024). Rapid eDNA survey reveals a unique biodiversity hotspot: The Corubal River, West Africa. BioScience, 74(6), 405-412. doi:10.1093/biosci/biae036
This article by Abhishyant Kidangoor was first published by Mongabay.com on 6 September 2024. Lead Image: One of the species that had previously not been recorded in the country is the Egyptian fruit bat (Rousettus aegyptiacus). Image by Simon Willison via Flickr (CC BY-NC 2.0).
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