Deep trouble Bobby Model/National Geographic

Loss of biodiversity in Lake Tanganyika, Africa’s oldest and deepest lake, has been driven by 500 years of sustained climate warming, a study of core sediments has found.

This has led to a decline in the abundance of the lake’s fish that pre-dates commercial fisheries.


We have known that the warming climate is transforming lakes worldwide, but a lack of consistent climate and fishery data from the tropics has meant that little was known about how lakes in the region were affected.

So Andy Cohen at the University of Arizona in Tucson and colleagues analysed sediment cores from Lake Tanganyika in East Africa to study proxies of temperature, algal production and abundance of fish fossils over the past 1500 years.

Lake Tanganyika’s surface waters are fertilised by an upwelling of nutrient-rich water during the windy season. The team found that rising temperatures have been preventing water layers from mixing.

This has reduced oxygenation in the lower water layers and cut populations of the algae, molluscs and crustaceans that the fish depend on by as much as 38 per cent.

Lake layers

This stratification kills productivity and narrows the oxygen-rich coastal habitat where most endemic species are found.

“As the climate warms it makes the surface of the lake warm,” says Cohen. “And Tanganyika being a deep tropical lake doesn’t mix every year as lakes in cooler climates do, instead the surface warmer waters mostly just sit on top of the cooler water below.”

Climate warming and intensifying stratification have almost certainly reduced potential fishery production, says the team.

They found a correlation between rising temperatures and declining biodiversity, which suggests that declines in the abundance of fish pre-date the establishment of commercial fisheries in the mid-20th century.

This means that while overfishing contributes to loss of biodiversity in Lake Tanganyika, which is renowned for the number of species that live in it, the temperature rise seems to be the main driver.

The ecological consequences of climate change for other lakes in Africa will depend on their shape and depth.

Other Great Lakes in the region, such as Lake Kivu and Lake Malawi, are likely to see a similar loss of diversity, says Cohen.

On the other hand, Lake Victoria has a shallow basin and hardly experiences stratification, so should be spared the same fate as Lake Tanganyika, says Melckzedeck Osore at the Kenya Marine and Fisheries Research Institute.

But it is hard to predict if and how lake life will survive in a warmer future, he says. Much will depend on genetics and how well different species adapt.

Osore calls for local people to be involved in mitigation measures, as those living alongside the lake may have a better understanding of the changes.

Journal reference: PNAS, DOI: 10.1073/pnas.1603237113

Read more: Many of world’s lakes are vanishing and some may be gone forever; Global browning: Why the world’s fresh water is getting murkier