In 2022, 350 African elephant carcasses were found in the northeastern sector of Botswana, known as the eastern Okavango Panhandle. As the timing was at the peak of COVID-19, there were poor holistic attempts to investigate the event.
Botswana is home to a third of all African elephants and is also a poaching hotspot. However, elephant carcasses with tusks intact demonstrate an event other than poaching. Another theory suspected virulent and bacterial causes; however, the absence of clinical signs waived off these claims as well.
Now, a new study conducted by researchers at King’s College London provides further evidence for those elephant deaths. Since the year was very wet, followed by a very dry one, toxic blooms of blue-green algae or cyanobacteria had developed in watering holes. Drinking from these water holes might have poisoned elephants.
Cyanobacteria are benthic or planktonic phototrophic prokaryotes abundant in stagnant and nutrient-rich waters. Several bloom-forming species cause harm with their toxin production. These blooms are prevalent with anthropogenic nutrient input and climate change.
“Botswana is home to a third of all African elephants, and this unprecedented die-off within their largest remaining population underlines the escalating concerns surrounding the impact of drought and climate change on the Okavango Delta, one of the most important ecosystems in the world,” says Davide Lomeo.
Cyanobacteria are common in southern Africa and have previously been linked to wildlife mortality events. An analysis in the journal Science of the Total Environment confirms that toxic algae is the cause.
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The team combined spatial analysis with satellite data to further study the connection between the algal blooms and elephants. The satellite data revealed the increased algal levels and repeated blooming events in 2020.
Data also revealed that the decayed elephant carcasses were more spread out than fresh carcasses. This indicated that this die-off is not the usual elephant mortality pattern.
“We identified 20 waterholes near fresh carcasses that experienced increased algal bloom events in 2020 compared to the previous three years combined. These waterholes also exhibited the highest average algal biomass of the period 2015 – 2023,” said Davide.
After drinking from the watering holes, elephants are estimated to have died within about 88 hours of exposure. This frequent presence of algal toxins suggests a significant threat to wildlife.
“Southern Africa is projected to become drier and hotter under climate changes, and as a result, waterholes across this region will likely be drier for more months of the year,” Davide adds.
“Our findings point to the potential negative effects on water quantity and quality, and the catastrophic repercussions on animals, this could have.“
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Journal Reference
- Lomeo, D., Tebbs, E. J., Babayani, N. D., Chadwick, M. A., Gondwe, M. J., Jungblut, A. D., McCulloch, G. P., Morgan, E. R., Schillereff, D. N., Simis, S. G., & Songhurst, A. C. (2024). Remote sensing and spatial analysis reveal unprecedented cyanobacteria bloom dynamics associated with elephant mass mortality. Science of The Total Environment, 957, 177525. DOI: 10.1016/j.scitotenv.2024.177525