The mysterious deaths of over 350 elephants in Botswana during 2020, initially baffling scientists and conservationists, have finally been attributed to a “toxic brew” of cyanobacteria-contaminated water. Researchers from King’s College London, in collaboration with other institutions, meticulously pieced together evidence pointing to toxic algal blooms in watering holes as the primary culprit. The sudden and clustered nature of the deaths, coupled with the intact tusks of the deceased elephants, effectively ruled out poaching or infectious diseases like anthrax. The investigation revealed that approximately 20 watering holes across a vast 6,000 square kilometer area of the Okavango Delta were contaminated with these toxic blooms.
Cyanobacteria, also known as blue-green algae, are microscopic organisms found in various aquatic environments. While not all species are harmful, certain types can produce potent cyanotoxins under specific conditions. These conditions include elevated water temperatures, nutrient loading, and changes in salinity. The toxins released by these blooms can be deadly to animals that ingest contaminated water. The research team, led by Davide Lomeo, an Earth observation scientist at King’s College London, used a combination of aerial surveys, satellite imagery, and epidemiological methods to unravel the mystery. Lomeo’s prior research on mass mortality events in African waterbodies proved instrumental in guiding the investigation.
The initial discovery of the elephant carcasses was made by Elephants Without Borders, a conservation organization conducting routine aerial surveys. The sheer number of carcasses and their concentrated distribution immediately signaled an unusual event. The survey identified 161 carcasses and 222 sets of bones, all within close proximity, suggesting a rapid and localized cause of death. This observation, combined with the absence of typical signs associated with poaching or disease, led researchers to investigate environmental factors, particularly the water sources used by the elephants.
The research team employed satellite imagery to track elephant movements and correlate their deaths with their proximity to watering holes. They found that many elephants perished within an average of 3.6 days (88 hours) after visiting contaminated water sources, a timeline consistent with previously documented cases of cyanotoxin poisoning in large mammals. The distance traveled by the elephants after drinking, approximately 16.5 kilometers, further supported the theory that the watering holes were the source of the fatal toxins. The study concluded that the elephants likely consumed lethal doses of cyanotoxins through repeated visits to contaminated waterholes, resulting in a fatal accumulation of the toxins in their organs.
Despite the strong evidence pointing to cyanobacteria as the cause, the investigation faced several challenges. The COVID-19 pandemic hampered timely sample collection, preventing definitive confirmation of cyanotoxin presence in the elephants’ tissues. The time lapse between the deaths and the aerial surveys also made it difficult to rule out the involvement of scavengers or other factors. Furthermore, the precise levels of toxicity in each watering hole remained unknown, as did the exact species of cyanobacteria responsible. This gap in information creates some uncertainty regarding the specific mechanisms behind the mass mortality event.
The researchers acknowledge the remaining uncertainties but emphasize the significance of their findings. The Botswana government officially attributed the deaths to cyanotoxin poisoning, acknowledging the study’s conclusions. However, the lack of tissue samples prevents a complete understanding of the specific toxins involved and their potency. The research highlights the potential dangers of cyanobacterial blooms in arid environments where animals rely on stagnant water sources. While this event focused on elephants, the study emphasizes the vulnerability of other animal species, including aquatic life, to similar toxic events.
The study’s findings have broader implications for conservation and ecosystem management. The increasing frequency of harmful algal blooms, often linked to rising temperatures and nutrient runoff, underscores the need for ongoing monitoring and mitigation strategies. The difficulty in detecting smaller animal deaths emphasizes the potential for undetected ecological damage from these blooms. Future research will focus on identifying the specific species of cyanobacteria involved, determining the precise environmental triggers for toxic blooms, and developing methods for early detection and prevention of such events. Ultimately, the tragic deaths of these elephants serve as a stark reminder of the interconnectedness of ecosystems and the potential for subtle environmental changes to have devastating consequences.
