Scientists prove Tasmanian wetland overtaken by rice grass can rebound

Walk the edge of Duck Bay in north-west Tasmania at low tide and what you notice first is the grass. Thick, waist-high, unbroken across what were once some of Tasmania's most productive coastal wetlands. No native samphire. No small fish working the shallows. But it was not always like this.

New University of Tasmania research, published in the journal Austral Ecology, has found that when this invasive grass is removed, these wetlands can recover, and faster than many expected.

The grass is rice grass, Spartina anglica, and it arrived with the best of intentions. Introduced deliberately from the 1930s to stabilize eroding banks, it was welcomed at the time. "Thousands of acres of valueless land could be converted into grazing country," the local Circular Head Chronicle reported in 1950.

But rice grass had no interest in staying where it was put. Dense and fast-spreading, it colonized saltmarsh and intertidal flats across the region, crowding out native plants and cutting off the habitat that estuarine fish depend on for feeding and shelter. By 2013, it had spread across more than 500 hectares of Duck Bay alone.

The Circular Head Landcare Group, a community organization that has been working to remove rice grass in the Smithton region since that year, has invested hundreds of volunteer hours in the effort, using a licensed herbicide applied by high-pressure hose, quad bike, backpack sprayer, and more recently, by drone. In 2019, new funding extended the work for a further five years, with Iona Flett leading project design and management.

Dr. Vishnu Prahalad and his colleagues from the University of Tasmania's School of Geography, Planning, and Spatial Sciences monitored what came next. Three years after treatment, the number of fish species recorded in restored areas had more than doubled, from five to eleven, and total fish numbers had increased roughly twentyfold.

At Morgans Bay, one of the two sites studied, fish had been almost entirely absent before treatment. By 2023, the team was recording 255 fish per 100 square meters, matching densities found in completely undisturbed saltmarsh nearby.

"Saltmarshes are incredibly productive ecosystems that support biodiversity, fisheries and coastal resilience," Dr. Prahalad said. "Our results show that when invasive species are removed, native systems can bounce back while also restoring fish access."

To understand what the returning fish were actually doing there, the team caught yellow-eye mullet, a species of commercial and recreational importance, and examined the contents of their stomachs. Every single one had been feeding, with evidence of recently eaten invertebrates, including amphipods and insects from the marsh surface.

The fish were not passing through. They were eating, which meant the marsh was functioning again as both a nursery and a feeding ground for the next generation of fish.

"Removing rice grass doesn't just open up space, it restores function," Dr. Prahalad said. "Seeing the fish return, feeding and sheltering in these wetlands again, that is what this work has always been about."

Flett said the findings have given the people who have spent years doing this work something they have long needed.

"People in this region have been working to get rid of rice grass for decades because they could see what it was doing to the coast," she said. "Having the University of Tasmania document the recovery so thoroughly means we can now show decision-makers and funders exactly what is possible. It turns local knowledge and hard work into evidence that carries weight."

The study is one of the first in the southern hemisphere to document what saltmarsh recovery looks like after eradication, not just plants returning, but the animals that depend on them.

Coastal saltmarsh is listed as a threatened ecological community under Australian national environment law, and rice grass invasion is one of the key pressures driving its decline.

The researchers note that some rice grass had begun to regrow in treatment plots by the final survey, and that recovery varied between sites. Restoration requires ongoing vigilance, not a single intervention. But the direction of travel is clear. For a wetland that spent the better part of a century being quietly overtaken, that is a meaningful start.

More information:
Vishnu Prahalad et al, Ecological Outcomes of Invasive Rice Grass (Spartina anglica) Removal for Restoring Native Saltmarsh Vegetation and Fish Habitat Function, Austral Ecology (2026). DOI: 10.1111/aec.70166

Provided by University of Tasmania