A scene from the 1040s, when rabbits were in plague proportions.

Rabbits have been identified as the culprit behind historical damage to the vast dune system that flanks South Australia’s Coorong.

A long-term study of vegetation cover on Younghusband Peninsula’s transgressive dunes by Flinders University researchers shows that rabbits have been the most destructive factor affecting dune stability, ahead of wind, temperature fluctuation or rainfall ¬- and recent reduction of the rabbit population has greatly improved the stability of these dunes.

“We had stopped the natural evolution of the dune system. With the introduction of rabbits, we destabilised a natural, functioning ecosystem and compromised the stability of the dunes,” says Professor Patrick Hesp, Strategic Professor in Coastal Studies at Flinders University and co-author of the new study.

However, Martim Moulton, PhD student working with Professor Hesp, Dr Graziela Miot da Silva and others found that the release of viruses to kill rabbits have turned these results on their head. Aerial photographs of the peninsula from 1949 to 2017 show that vegetation cover has significantly increased in recent years, and stabilised the dunefields, since the rapid decrease of rabbit populations.

“Convention would suggest that strong vegetative growth is the result of increased rainfall and reduced winds, but that simple notion doesn’t apply in the Younghusband Peninsula. The wind records are too variable, for starters, so something else had to be a key contributing factor to significant changes in vegetative growth – and we found out that it’s all about the bunnies.”

Historical records show that strong rains during spring accelerate vegetation growth in the Younghusband Peninsula dune system, but they also boost rabbit populations – which, at their worst, reached an alarming 26 rabbits per hectare and resulted in a critical reduction in vegetation coverage of the dunes.

Subsequent peaks in vegetative growth on the dunes through more than 65 years of records corresponds with the introduction of specific viruses that dramatically reduced rabbit populations – myxomatosis in 1952, the rabbit flea in 1968, Rabbit Haemorrhagic Disease in 1995, and a combined virus in 2018, which has had 40 per cent effect on already low population numbers.  

The paper – “Changes in vegetation cover on the Younghusband Peninsula transgressive dunefields (Australia) 1949-2017”, written by Martim Moulton, Patrick Hesp, Graziela Miot da Silva, Camille Bouchez, Muriel Lavy and Guilherme Fernandez – is published in journal Earth Surface Processes and Landforms (DOI: 10.1002/esp.4508)

The findings have significance for international concern about the protection of vulnerable coastlines, with Professor Hesp saying this study underlines the need to examine the prevalence and impact of introduced plants and pests in an ecosystem. “We’ve shown that removing the introduced species will greatly help the stabilisation of an affected coastal dune system,” he says.

While Professor Hesp notes the Younghusband Peninsula dunefield is currently in a good state, the system is still fragile and vulnerable to further damage if rabbits return to the area in large numbers.

“We can see the impact they have made on the environment, so we have to make sure that the bunnies don’t come back – because we now know what the consequences will be,” says Professor Hesp.

“We must keep a close eye on rabbit population growth, because they are the trigger to vegetation destruction in the dunes.”