Scientists surprised to discover mayflies and shrimp making their bodies out of ancient gas

by bpckle | May 2, 2025 | Media

What’s the currency for all life on Earth? Carbon. Every living thing needs a source of carbon to grow and reproduce. In the form of organic molecules, carbon contains chemical energy that is transferred between organisms when one eats the other.

Plants carry out photosynthesis, using energy from sunlight to convert carbon dioxide and water into sugar and oxygen. Animals get carbon by consuming organic matter in their diet – herbivores from plants, carnivores from eating other animals. They use this carbon for energy and to produce the molecules their bodies need, with some carbon dioxide released by breathing.

But there are other, stranger ways of getting carbon. In our new research, we found something very surprising. River animals were feeding on methane-eating bacteria, which in turn were consuming fossil fuel as food.

Usually, the carbon used as food by river creatures is new in the sense it has been recently converted from gas (carbon dioxide) to solid carbon through photosynthesising algae or trees along the bank. But in a few rivers, such as the Condamine River in Queensland, there’s another source: ancient natural gas bubbling up from underground, which is eaten by microorganisms. Insects such as mayflies have taken to this methane-based carbon with gusto.

How does a river usually get its carbon?

The way photosynthesised carbon moves from a plant to an animal and then another animal can be described as a food web. Food webs show the many different feeding relationships between organisms, and show how species depend on each other for sustenance in an intricate balance.

In a river food web, carbon usually comes from one of two sources: plants growing and photosynthesising in the river (such as algae), or when organic matter such as leaves are washed in by rain or blown in by wind.

Rivers that are well connected to their floodplains often get plenty of carbon from leaf litter from trees which dissolves in water or is eaten directly by animals. Algae in rivers provide a high-quality source of carbon for animals because they can contain high concentrations of omega-3 fatty acids essential for growth and reproduction. The primary source of carbon for river animals varies depending on prevailing conditions and the individual river.

The carbon of the Condamine

Some microorganisms called archaea naturally produce small amounts of methane in oxygen-depleted sediments of rivers.

But we wanted to look at the Condamine to see whether much larger volumes of methane could be used as food.

After it forms deep underground, natural gas can slowly escape through cracks in the earth. If a river bed is directly above, this methane-rich gas will seep into the river.

That’s what happens in Queensland’s Condamine River. The river rises on Mount Superbus, inland from Brisbane, and flows inland until it meets the Darling River.

In some parts of the river, methane bubbles up constantly through the water column from a natural gas reservoir that formed since the Late Pleistocene.

In these stretches of river, dissolved methane concentrations are extremely high: up to 350 times greater than trace concentrations upriver, away from the methane seep.

We wanted to see whether methanotrophic bacteria consuming methane from natural gas were being eaten by river animals, and whether we could trace the carbon signature through the food web.

To find out, we analysed the carbon in the bodies of river animals such as zooplankton, insects, shrimp, prawns and fish, and compared it to the different sources of carbon that could make up their food.

The results were clear: animals within reach of the natural gas seeping from underground had a distinct carbon signature showing they were eating food derived from the natural gas. In fact, for insects such as mayflies, methane-based food made up more than half (55%) of their diet.

Over time, this methane-derived food moved up the food web, showing up in prawns and even fish. Here too, it contributed a significant portion of their carbon.

We found this methane–derived carbon moved through multiple levels of the local food web. It made up almost a fifth (19%) of the carbon in shrimp and 28% of the carbon in carnivorous fish.

For river shrimp and prawns, leaves washed into the river were still important sources of carbon. For mayflies, algae was still an important source of food.

But our work shows that natural gas seeps can be a major, even dominant, source of energy for the entire food web. This is very surprising. It shows an unexpected connection between Earth’s geology and living creatures in a river.

Why does this matter?

Until now, researchers have focused on river and land plants as the main way a river gets its carbon. Our research has uncovered a surprisingly significant way some rivers get their carbon – methane.

In deep sea research, this pathway is better understood. Methane-eating bacteria can form the basis of entire ecosystems which have sprung up around deep sea hydrothermal vents of hot water.

But until now, we have overlooked the role methane-eating bacteria can play in rivers. With this knowledge, we can better track the flows of carbon in rivers so we can gauge ecosystem productivity and see how a food web is functioning.

Paul McInerney receives funding from the Commonwealth Environmental Water Holder.

Logging devastated Victoria’s native forests – and new research shows 20% has failed to grow back

by bpckle | May 2, 2025 | Media

Following the end of native logging in Victoria on January 1 2024, the state’s majestic forests might be expected to regenerate and recover naturally. But our new research shows that’s not always the case.

We quantified the extent of regeneration following logging in the eucalypt forests of southeastern Australia between 1980 and 2019. This included nearly 42,000 hectares of logged mountain ash forest in Victoria’s Central Highlands.

We analysed satellite data, logging records, on-ground surveys and drone photography, and discovered that nearly 20% of logged areas failed to regenerate. This represents more than 8,000 hectares of forest lost. All that remains in these areas are grassy clearings, dense shrublands or bare soils.

We also found the rate of regeneration failure has increased over the past decade. While failure was rare in the 1980s, it became much more common over time – affecting more than 80% of logged sites by 2019.

These regeneration failures weren’t random. They were found mostly in close proximity to each other, on areas with steep slopes, relatively low elevation, and where the area of clear-felled forest was long and narrow.

Our research shows more needs to be done to restore Victoria’s forest after logging.

Restoring majestic forests and their vital services

Victoria is home to some of the most spectacular forests on the planet. They include extensive stands of mountain ash, the tallest flowering plant on Earth, which can grow to almost 100 metres in height. Alpine ash, another giant, can grow up to 60m tall.

These forests have great cultural significance to Indigenous people and support many recreational and tourism activities.

Healthy forest ecosystems also deliver clean water and carbon storage services. In fact, mountain ash forests contain more carbon per hectare than most other forests around the world.

But Victoria’s forests have long been logged for timber and pulp. The main method of logging – clearfelling – scars the landscape, leaving large areas devoid of trees if natural tree regeneration fails.

Mountain ash is especially vulnerable

Our research revealed 19.2% of areas logged between 1980 and 2019 in our study area (8,030ha out of 41,819ha cut) failed to regenerate naturally.

We also found strong evidence of a significant increase in the extent of failed regeneration over 40 years, increasing from less than two hectares per cutblock in 1980 (about 7.5%) to more than nine hectares per cutblock in 2019 (about 85%), on average.

We found regeneration failure was more likely in mountain ash forests compared with other forest types.

This adds to the case for listing the mountain ash forests of the Central Highlands of Victoria as a threatened ecological community.

A responsibility to restore

Under Victoria’s Code of Forest Practice for Timber Production, logged native forests must be properly regenerated within two to three years of harvest.

That’s because it is nearly impossible for the native forest to regenerate after three years without human intervention. The young trees face too much competition from grass and shrubs.

These degraded areas no longer hold the value they once did and they cannot provide the same level of ecosystem services such as carbon storage, water purification, or habitat for wildlife.

With no current government restoration plan, these landscapes will remain degraded indefinitely. The Victorian government retains legal responsibility to restore these degraded forests, but currently lacks any large-scale restoration strategy, making action urgently required.

A way forward: using green bonds to fund regeneration

Our research shows the regeneration of forests after logging is not guaranteed. Nature often needs a helping hand. But we need to find ways to fund these projects.

Globally, governments have used “green bonds” to lower the cost of borrowing tied explicitly to measurable environmental results.

Victoria already has green bonds “to finance new and existing projects that offer climate change and environmental benefits”. But funds are typically used to finance investments in transport, renewable energy, water and low carbon buildings.

As part of a coalition of researchers, environmental organisations, and finance sector partners we proposed a A$224 million green bond for forest regeneration. This proposal was put to the Victorian government via the Treasury Corporation of Victoria.

Green bond funding would help leverage co-investment from the Commonwealth government and philanthropic partners to improve monitoring and biodiversity outcomes in native forests.

As part of the proposed green bond, areas of logged forest where natural regeneration has failed would be restored.

Other investments under the green bond could include creating tourism ventures (and associated jobs), controlling feral animals such as deer, and biodiversity recovery – creating habitat for endangered species such as the southern greater glider and Leadbeater’s possum, for example.

The $224 million required for the ten years of the green bond — or around $22.4 million per year — is less than the substantial losses Victoria incurred on its investment in VicForests over the past decade.

Our research suggests leaving nature to its own devices would mean losing a fifth of the forests logged over the past 40 years. Bringing the trees back has multiple benefits and would be well worth the investment.

Maldwyn John Evans receives funding from the Australian Government.

David Lindenmayer receives funding from The Australian Government, the Australian Research Council and the Victorian Government. He is a Councillor with the Biodiversity Council and a Member of Birdlife Australia.

Chris Taylor does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.