New paper reveals unprecedented algal bloom linked to the 2020 mass mortality of African elephants

Image caption: African elephants around a seasonal pan, Botswana. Image credit: Dr Amanda Stronza

Davide Lomeo, Earth Observation Science PhD researcher at King’s College London, Plymouth Marine Laboratory and the Natural History Museum, has published a paper as part of his PhD thesis ‘Remote sensing and spatial analysis reveal unprecedented cyanobacteria bloom dynamics associated with elephant mass mortality’ in Science of the Total Environment. 

His study revisits the mass mortality of over 350 African elephants in 2020, which saw carcasses clustered near waterholes in the north-eastern sector of Botswana. 

The deaths occurred during the peak of the COVID-19 pandemic, and as a result, attempts to respond to and investigate the event were hindered. Whilst the area is a known poaching ‘hotspot’, this was ruled out since the elephants were found with tusks intact. Other initial theories included viral and bacterial causes, such as the encephalomyocarditis virus or anthrax, but evidence collected in the field deemed both unlikely. 

The suspected cause of the die-off had been officially attributed by the Government of Botswana to cyanobacterial toxins in 2020, but evidence remained inconclusive.  

Aquatic cyanobacteria are known for their highly visible blooms that can grow in both freshwater and marine environments, and can form a blue-green appearance. Some bloom-forming species produce toxins and accumulate at the water surface, forming concentrated ‘scums’ which can be harmful to health. Such blooms frequently lead to the closure of recreational waters when spotted. 

In the study, Davide combined remote sensing and extensive spatial analysis – integrating the distribution of elephant carcasses documented during a post-mortality aerial survey – and satellite data on the location and condition of around 3000 regional waterholes. 

The study identified 20 waterholes near fresh carcasses that also exhibited evidence of dense blooms in 2020. 

Graphical Abstract: Remote sensing and spatial analysis reveal unprecedented cyanobacteria bloom dynamics associated with elephant mass mortality 

Davide commented: 

“The waterholes experienced more cyanobacteria blooms during the period of the mortality event than in any other period in the past nine years. This is likely linked to the succession of an extremely wet 2020, from an extremely dry 2019, providing ample nutrients for heavy blooms. The distribution of the elephant carcasses across the landscape suggests a strong spatial link with waterholes of dubious water quality.” 

“Globally, this event underscores the alarming trend of sudden, climate-induced diseases affecting large ungulates, reflecting the broader, devastating impacts of climate change on biodiversity and ecosystem health.” 

Image: Decaying algal accumulation (and scum) in the stagnating waters of a waterhole in Botswana – photo credit: Davide Lomeo. Cyanobacteria are likely present due to their dominance in turbid, stagnating waters, especially if waters have higher salinity and are very warm.  

Image: Elephant wading into the waters of the Okavango Delta to drink – image credit: Davide Lomeo. Davide adds, “This was not taken from a pan, but from the Okavango Delta itself. The reason it may be relevant is that elephants will prefer drinking fresh water from the Delta if the can. If they do not have direct access, then they are ‘forced’ to drink the water from surrounding pans, which may hold a higher likelihood and risk of cyanobacteria presence (and potentially cyanotoxins)”. 

One of Davide’s PhD supervisors, Professor Stefan Simis – an Earth Observation scientist at PML whose research focuses on inland and coastal water quality, commented: 

“Davide’s paper highlights the devastating impacts of harmful algal blooms, whilst also demonstrating the urgent issue of water quality monitoring, even in the smallest of natural water bodies.” 

“Using spatial analysis to identify the source of poisoning or infection has a very long history – schools still teach the example of John Snow’s map of cholera outbreak in 19th century London.” 

“Davide’s work, conducted in collaboration with the local authorities, shows how satellites can be used to identify multiple sources of contamination. It shows that we need to keep pushing the envelope on satellite observations, to allow a timely response should the situation repeat.” 

The research also involved colleagues from the University of Botswana, the Natural History Museum, London, and Queen’s University Belfast. 

Access the paper ‘Remote sensing and spatial analysis reveal unprecedented cyanobacteria bloom dynamics associated with elephant mass mortality’ here >>