A team of researchers and native rangers have discovered why the Gulf of Carpentaria is a dugong hotspot by conducting a major study of its seagrass beds, which face multiple threats from climate change.
- Scientists have been surprised by the extent and diversity of seagrass beds in the Gulf of Carpentaria
- Research has helped identify where increased protection is needed
- Dugongs face imminent threat as warming seas damage seagrass beds
New research by the team has revealed that seagrass beds along the Limmen region of the Gulf in the Northern Territory are more widespread and diverse than previously thought.
Dugongs, classified as a vulnerable species, feed almost exclusively on seagrass.
One of the research project leaders, Rachel Groom of Charles Darwin University, said scientists and the Marra people of the Limmen region have long known that the Gulf is home to one of the largest dugong populations in the world. world, numbering up to 5,000, or half of the total NT population.
This is only eclipsed by the Torres Strait, which has around 15,000 dugongs.
“There are a lot of sea turtles that depend on habitats in the Limmen region, and it’s also the most important habitat for dugongs in the Northern Territory.”
Dr Groom’s colleague, Alex Carter of James Cook University, said the team had spent weeks surveying more than 3,000 seagrass sites across 2,250 square kilometres.
“What we found were vast seagrass meadows that grew near mangroves in very shallow water, which exposed at low tide and then plunged into deep water at 20 meters,” said she declared.
“We mapped some very large grasslands and they were much more diverse than expected – we had eight species in total.”
The new research was co-funded by universities and the governments of the Northern Territories and Canada, as well as the Li-Anthawirriyarra Sea Rangers who helped carry out the survey.
Ranger Shaun Evans said the work to better establish the biodiversity significance of the area was very important to his Marra people.
“All the animals that live in the ocean are important to our cultural side, like the dugong and the turtle, the stingrays, [that] applies to all animals living in the ocean,” he said.
Scientists hope the work will lead to increased protection
Only part of the study area is already protected from mining, shipping and commercial fishing, as it is part of two marine parks of the Northern Territories and the federal government.
Dr Groom said the scientists hoped their research would demonstrate to both governments where protections were not currently broad or strong enough.
“What this project has done is really get a better understanding of where the priority areas to protect are, and I think some of those areas are just non-negotiable conservation areas,” she said.
She said protecting the area is particularly important for her dugongs because they don’t move elsewhere to feed.
Dr. Groom’s work in tagging Limmen’s dugongs with native sea rangers helped establish this.
“The Gulf, and in particular the Limmen and Sir Edward Pellew Islands areas, are really important to these animals because they don’t tend to travel very far – they don’t go to the east coast of Queensland or into Western Australia,” she said.
Dr Carter said she hoped the team would be able to expand the research.
“This study is really one piece of the puzzle of understanding seagrass habitats in northern Australia, so we hope to continue these investigations over a wider area to better understand how they are connected, and we also hope that ‘It will lead to long-term monitoring by the rangers,’ she said.
Seagrass beds suffer from the impacts of climate change
Dr Groom said the biggest threat to dugongs and their seagrass habitat was climate change.
“The Gulf has one of the highest rates of sea level rise in Australia, at 9mm per year, and there is also evidence that seagrass beds can be burned, particularly when they are exposed at low tide,” she said.
“By all means we can act locally to ease the pressure on some of these resources, but overall we need to have greater commitment from the leaders of world governments.”
The Gulf Coast has suffered major impacts from climate change in recent years, including the massive die-off of thousands of miles of mangroves in 2016.
CSIRO Oceans and Atmosphere researcher Eva Plaganyi studies how the impacts of climate change, including rising sea temperatures, are affecting seagrass beds in the Gulf of Carpentaria and Torres Strait and the animals that dependent on it for 13 years.
“In tropical waters a lot of seagrass beds and animals are close to their thermal tolerance limits, for example seagrass beds can only withstand about 35 degrees Celsius, so there is a time when seagrass beds start to die for,” she said.
Dr Plaganyi said that over the past century the average sea temperature in the Gulf has risen by 1 to 1.5 degrees Celsius.
“And there were massive spikes in temperatures at times, including March 2016 when the average temperature rose 2.5 degrees,” she said.
“And of course, if the seagrass beds die, the dugongs that feed on them and other animals like turtles, all the fish and crabs and other organisms that live on the seagrass beds will also be affected.”
Dr Plaganyi said another big concern for these habitats was that stronger and more frequent cyclones would destroy seagrasses and changes in ocean currents would kill them by covering them with sand.