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Wildfire ash threatens to wipe out many aquatic species

While the effects of wildfires on terrestrial ecosystems are well-documented, the impact of wildfire ash on aquatic life has only recently begun to be understood. 

However, a team of scientists led by the University of Alberta has now explored the deadly consequences of wildfire ash on Australian water ecosystems.

More frequent and intense wildfires

As climate change exacerbates the frequency and intensity of wildfires, Australia faces increased vulnerability to bushfires. 

“Therefore, many Australian species may be threatened by fires,” said Jenelle McCuaig, a masters student at Alberta. “This is putting them at greater risk of endangerment and possible extinction.”

Contamination from wildfire ash

Wildfires release ash that can enter aquatic environments directly or through runoff during rainfall. 

“Once in the water, ash may leach metals and organic combustion products, where they can affect organisms, acquired by ingestion through intestines or respiration through gills,” McCuaig explained. 

This contamination poses risks not only to aquatic life but also to human health, as freshwater ecosystems are vital sources of water and food.

Focus of the research 

McCuaig and her team concentrated their study on two common Australian crustacean species: a crayfish (Cherax destructor) and a shrimp (Macrobrachium australiense). 

The researchers exposed each species to varying ash concentrations to assess their sensitivity and survival likelihood. McCuaig then measured oxygen consumption using a respirometry system and took tissue samples to analyze metabolic activity.

Impacts of wildfire ash 

Their findings were alarming. Exposure to just 5g of ash per liter of water resulted in 100% shrimp mortality, while it required eight times this amount to achieve the same effect on crayfish. “The huge difference in sensitivity between the two species was much greater than I expected,” McCuaig said.

Thus, even closely related species can exhibit vastly different responses to environmental stressors like wildfire ash. 

“Differences in body shape and gill structure, as well as habitat preferences, has allowed them to fulfill different niches. Crayfish demonstrated greater resilience to the ash exposure compared to the shrimp,” McCuaig added.

Severe physiological stress 

For the surviving crayfish and shrimp, those exposed to the highest ash concentrations exhibited the highest metabolic rates, indicating severe physiological stress. 

“This is particularly concerning during ash exposure because increased ventilation means that the animals will be taking up more of the ash particles and leached contaminants from the water, further affecting their body systems.”

McCuaig emphasizes the importance of this research in identifying species most at risk from wildfires, which can guide breeding programs or relocation efforts. “When it comes to wildfires, resources are limited, so we must prioritize response actions,” she explained.

“Species conservation begins with wildfire prevention in the first place – it is incredibly important to be educated about, and to implement, fire-safety into our lives to mitigate human-caused wildfires,” she concluded. 

2019-20 Australian bushfires

WWF Australia noted that the 2019-20 Australian bushfires were catastrophic in scale and impact – for both people and nature.

“Up to 19 million hectares was burnt, with 12.6 million hectares primarily forests and woodlands. Nearly 3 billion animals were impacted by the blazes,” stated WWF Australia. “But even before the bushfires started, our native forests and wildlife were suffering due to deforestation and the impacts of climate change on the environment.”

“Australia is home to incredible biodiversity that is found nowhere else on the planet. But now, more than 1,700 species of plants, animals and ecological communities are officially listed as threatened. This includes nearly 500 species of wildlife. The bushfires during the summer of 2019-20 only made the situation worse.”

The University of Alberta study will be presented at the Society for Experimental Biology’s annual conference in Prague.


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