A recent study has shed more light on the tragic deaths of 350 African elephants in Botswana in 2020, linking them to toxic algae found in water holes that had surged due to climate change.
A recent study led by King’s College London has shed more light on the tragic deaths of 350 African elephants in Botswana in 2020, linking them to toxic algae found in water holes that had surged due to climate change.
The primary author of the report indicated that their findings suggest the elephants were likely poisoned by water holes with toxic blooms of blue-green algae, also known as cyanobacteria, which emerged following a wet year after prolonged dryness.
Davide Lomeo, a PhD student from the Department of Geography at King’s College London and co-supervised by Plymouth Marine Laboratory (PML) and the Natural History Museum, stated, “Botswana is home to one-third of all African elephants. This unprecedented mortality within its largest remaining population raises serious concerns about the effects of drought and climate change on the Okavango Delta, one of the world’s most vital ecosystems.”
The first elephant carcasses were discovered in the north-eastern part of the Okavango Delta between May and June 2020, but poaching was quickly ruled out as the cause of death.
This incident raised alarm worldwide, with a total of 350 elephants confirmed dead.
Toxic substances produced by algae in the waterholes were one of the suspected causes, although evidence was inconclusive at the time—partly due to the restrictions of the COVID-19 pandemic, which hindered sample collection.
The deaths of 25 elephants in nearby Zimbabwe from septicaemia during the same year put further doubt on the theory that algal toxins were responsible for the deaths in Botswana.
Nevertheless, in a paper published in the journal Science of The Total Environment, the researchers assert that their analysis strongly indicates toxic algae as the cause.
By integrating satellite data with spatial analysis, the team explored the connection between about 3,000 waterholes and the locations of the deceased elephants.
Their findings showed that the waterholes near where the elephants were found had higher levels of algae and a series of bloom events in 2020 compared to previous years—especially during the time linked to the mass die-off.
The researchers also noted that decayed carcasses were more spread out across the landscape than fresher ones, signifying that the 2020 mass die-off was not typical for elephant mortality.
“We identified 20 waterholes close to fresh carcasses that underwent increased algal bloom events in 2020 compared to the combined data from the previous three years. These waterholes also recorded the highest average algal biomass from 2015 to 2023,” said Davide.
After consuming water from these toxic spots, elephants were estimated to have traveled around 16.5 km before dying approximately 88 hours later.
These results point to a heightened risk and likelihood of harmful algal toxins in these waterholes, he added.
The team believes that the drastic change from a very dry 2019, the driest in decades for the region, to an exceptionally wet 2020 may have stirred significant sediments and nutrients from below, leading to the extraordinary algal growth.
Davide remarked: “Southern Africa is expected to become increasingly dry and hot due to climate changes, leading to waterholes being drier for longer periods of the year. Our findings highlight the potential negative impact on both water availability and quality, as well as the devastating effects on animal populations.”
“This research, in cooperation with local authorities, highlights the serious ecological consequences linked to harmful algal growth and emphasizes the imperative for thorough surveillance of water quality in all bodies of water, including the smallest ones. The study illustrates how satellite detection can be valuable in identifying various contamination sources, underscoring the need to enhance Earth observation capabilities for prompt action against similar environmental threats in the future.”
The research also involved collaboration with institutions such as the University of Botswana, the Natural History Museum in London, Queen’s University Belfast, and the Plymouth Marine Laboratory (PML).
