Looking beyond the headlines: How did snails fare in the 2019-2020 bushfires?

A new study by Australian Museum researchers sheds light on the impacts of the 2019-2020 wildfires on land snails in north-eastern NSW.

The wildfires of 2019/20 engulfed vast areas with unprecedented scale and ferocity. Apart from the tragic impacts on human lives, many Australians were also extremely worried about the possible damage these fires caused to our natural environment.

While the fires were still raging, conservationists and scientists scrambled to understand how dire the situation really was for the thousands of species that lived in the path of the devastation, which of them needed help most urgently, and what needed to be done to prevent the worst outcome – the extinction of a large number of native species. To get a better handle on the likely impact of the fires, several studies aimed to predict which species of plant and animal were most at risk by overlaying the extent of the fire zone with the extent of their known distribution. This exercise resulted in a list of more than 300 animal species that were of particular conservation concern.

In a second step, the Australian government responded by promoting specific research projects to document the possible damage caused by the fires on these priority species in more detail, so that help could go where it was most needed. Researchers from the Australian Museum partnered with scientists from the University of New South Wales to investigate the impacts of the wildfires on 26 species of land snail in north-eastern NSW, as well as on several species of beetles (read the AM blogs here and here).

Why land snails?

New South Wales is home to around 600 species of land snails, which exclusively inhabit relatively pristine natural habitats that have not been cleared, such as national parks and state forests. Most of these species have relatively small distributions, which makes them particularly vulnerable to localised disturbances. The notoriously slow pace of going about their every day lives also means that unlike many other animals, land snails cannot escape from a fire. All these factors render snails particularly vulnerable on the one hand and as good indicators to estimate the actual fire impact on wildlife on the other.

Hot on the heels of the bushfires, we set out to the Gondwanan rainforests of north-eastern NSW to investigate. We searched 70 sites, spending about three hours at each site, carefully searching the places where land snails are known to hide – under logs, barks, and rocks, and in crevices. We also collected a bag full of leaf litter from each site and set up a mobile field laboratory to pick up micro-snails under a microscope. We noted how burnt each site was so that we could compare the land snails between the sites. All these efforts culminated in a complete list of land snail species we have encountered alive or dead for each of these sites, shedding light on their survival in the aftermath of the bushfires.

Surprisingly, we found results that are contrary to the initial dire warnings of the impact the bushfires had on land snails. First, we found that most of the sites thought to be severely impacted by the fires and as the primary habitats of land snails, were actually a mosaic of areas with variable burn severities – with rainforests lightly burnt or unburnt.

Second, we attempted to visit as many sites as possible where species have been historically reported. This effort proved to be challenging as not long into our fieldwork, we realised many of the trails and tracks to the original sites have changed over the decades since the last time scientists had trodden these paths. For example, some former state forests have since become national parks and former logging tracks have gradually regrown with lush vegetation. Furthermore, fieldwork in the middle of a long La Nina season means many roads became inaccessible after rains, floods and landslides. Nevertheless, we managed to find live or fresh dead specimens for all target species, with representative individuals at almost 60% of the sites, thus re-confirming the survival of the 26 species after the fires.

While this shines a positive light on the survival of these species, we still assessed 3 species of conservation concern and 7 species as near threatened by the direct impacts of the 2019-2020 bushfires. This is based on their small distribution ranges, decline in habitat size due to the fires and the possibility of continuous decline in their habitat quality in the future.

The timeless adage that research uncovers more questions than answers applies to our study as well. In the course of this study, we realised than most of Australia’s land snails are not well understood. Beyond the handful of research articles and a few lines of information on museum specimen labels left by previous researchers, we know little about where they live and shelter, how they respond to environmental changes and how wide their distributional ranges truly are. The fires may also have caused changes in the snails' habitat structure and ecosystem dynamics. How such processes will affect the snails in the mid- to long-term remains a mystery.

Thus, every field trip helps us build a better impression of their habitats, microhabitats and distribution. We hope these data, now published in our new research article, can inform the formulation of important research questions that helps monitor and study these endemic species to ensure their survival in the longer term.

Dr Frank Köhler, Principal Research Scientist, Malacology, Australian Museum; Adjunct Associate Professor, UNSW.

Junn Foon, Research Associate, Malacology, Australian Museum.