Did toxic algae kill hundreds of elephants in Botswana? , wildlife news

Investigations into the sudden deaths of at least 350 elephants in Botswana in 2020 revealed that the cause was almost certainly a “toxic mixture” of open waters contaminated by a species of cyanobacteria, which released cyanotoxins, which essentially killed the elephants. Used to contaminate water holes.

According to researchers, about 20 water holes across about 6,000 square km (2,316 square miles) in Botswana’s Okavango Delta were contaminated.

So what happened, and how?

What is cyanobacteria and how does it harm elephants?

Although not all cyanobacteria, commonly known as blue-green algae, are toxic, some cyanobacteria can produce a type of deadly algal bloom (HAB) in standing water. This is the type that was discovered in an investigation conducted by researchers at King’s College London.

The study showed that African elephants (Loxodonta africana) died in May and June 2020 after drinking from water holes contaminated by these toxic algal blooms.

“Scientists believe that cyanotoxin production is related to certain environmental triggers, for example, sudden increases in water temperature, nutrient loading, salinity,” said David Lomeo, Earth observation scientist at King’s College London, Plymouth. An associate of the Marine Laboratory and the Natural History Museum in London and lead researcher of the recent study told Al Jazeera.

How was the death of elephants revealed?

In early mid-2020, a series of routine aerial surveys conducted by helicopter by the conservation organization, Elephants Without Borders, revealed several elephant carcasses scattered across the landscape of the Ngamiland district of northern Botswana.

The aerial survey showed 161 elephant carcasses and 222 bone sets, while also counting 2,682 live elephants in the eastern region of the Okavango Panhandle. Furthermore, the distances between the dead elephants indicate that the deaths were sudden rather than gradual.

“The strong clustering of carcasses also suggests that the event was sudden, with limited dispersal of the elephants before death,” the study authors said.

How did researchers identify toxic algae as the cause of death?

Before researchers could confirm that it was toxic algae that killed the elephants, they had to rule out several other possible causes.

“Although this area is a known poaching hotspot in Botswana, it was ruled out as the elephant carcasses were found intact,” the study authors said.

Other early theories included toxic and bacterial causes, such as encephalomyocarditis virus or anthrax, but evidence taken from the field – such as the age of the dead elephants and the absence of any clinical signs of the disease, meant that Researchers rejected these. Reason.

The distribution of bodies and bones suggested a unique “spatial pattern”, which indicated that local factors may have played a role in the mass deaths. This led to further exploration of the specific environmental and ecological conditions in the affected areas.

There were several other factors that served as evidence that the elephants’ drinking holes were to blame. Using satellite photographs, researchers measured the distance elephants walked after drinking from water holes – an average of 16.5 km (10.2 mi). Shortly thereafter, about 3.6 days (88 hours), several elephants died after drinking water from nearby contaminated water holes.

The report said 88 hours aligns with toxicological timelines previously reported for other large mammals dying from blue algae poisoning.

Additionally, Lomio’s doctoral work examining the history of mass mortality events in Africa and water quality in water bodies served as evidence to further the theory of water pore contamination.

“That incident sparked the idea, because it was a well-covered news story at the time, but no one really knew why he died. I then applied my skills in geospatial and computational data science to investigate the phenomenon under a well-known set of methods commonly applied in epidemiological investigations (e.g. COVID-19),” Lomio explained.

What is still unknown about the death of elephants?

It is impossible to measure toxicity levels for each waterhole from aerial photographs. Furthermore, according to the researchers, it is not clear whether the elephants drank from one water hole or from several.

“It is highly likely that he drank alcohol from several pans before his death. It cannot be established whether fatal intoxication occurred in a single drinking event, but it seems more plausible that if cyanotoxins were present and were the cause of death, it was through bioaccumulation of the toxins in the elephants’ organs. Was,” the study said.

Although it is clear that toxic reservoirs were the likely source of the mass death of elephants, there remains some uncertainty about the findings due to the timing of the mass death.

“The incident occurred during COVID-19 movement restrictions, and timely intervention was not possible. Therefore, tissue samples (which would confirm the presence/absence of cyanotoxin) were not collected. Post-mortem examination must also be done within a certain time frame, after which the samples will have deteriorated greatly. Additionally, cyanotoxins cannot be detected from satellites, so the links can only be indirect,” Lomio explained.

Since the aerial data was collected long after the deaths – in March and May 2020 – researchers could not definitively rule out the involvement of other animals in the elephant deaths.

Additionally, aerial surveys may have missed small organisms, potentially limiting scientists’ understanding of the full scope of the event.

“The area is famous for very high hunting rates, meaning that animal carcasses quickly disappear due to scavengers such as hyenas and vultures. Therefore, involvement of other animals cannot be ruled out,” Lomio said.

The specific conditions that would produce levels of toxicity in a watering hole that would be lethal to nearby animal species are still unknown.

“There is still uncertainty. We know that certain cyanobacteria species are more likely to produce cyanotoxins, and we know what toxins each species typically produces,” Lomio said.

According to research, cyanotoxins exhibit significant variation in their potency and effects. Some types are extremely toxic, capable of causing death even in very low concentrations. Others, although less immediately dangerous, may still pose a high level of health risk without necessarily being fatal. The field of cyanotoxin research remains an active one, with many aspects still to be fully understood and discovered.

Despite this, the overall findings of the study have been widely accepted. “The government of Botswana has officially attributed the deaths to environmental poisoning by cyanobacterial toxins, also known as cyanotoxins,” the study authors said.

Can this happen again?

Although mass deaths of elephants are rare, researchers cannot be certain that it will not happen again and that it will only affect elephants or land animals.

“All arid systems, where animals depend on stagnant water in lakes/ponds, are vulnerable to this (mass die-off), aquatic life in lakes can also be harmed in a similar manner. We’ve also seen it in rivers and oceans, where higher nitrification from agricultural runoff coupled with rising temperatures is causing destructive bacteria to thrive,” said George Wittemeyer, a behavioral ecologist at Colorado State University, one of the institutions involved in the study in Kenya. Al Jazeera reported that it turned out that elephants use different names.

Although it was relatively easy for researchers to identify elephant carcasses from the air due to their size, it would not be so easy to identify the sudden death of smaller animals.