Shark Bay in Western Australia is far away from everything: Perth is more than 700 kilometers from the idyllic bay, the small town of Broome is almost 1300 kilometers away. In a way, time seems to have stood still on the coast of lonely Western Australia. One of the few examples of living fossils is found in the bay: the stromatolites. They take visitors back to the beginnings of the earth’s history.
In this respect, the news that Australian researchers announced on Wednesday is perhaps less surprising. They believe they have also discovered what is believed to be the world’s largest plant in said Shark Bay – an ancient and incredibly hardy seagrass that stretches over 180 kilometers in length and is estimated to be at least 4500 years old.
Researchers from the University of Western Australia and Flinders University in Adelaide have published a study of the plant in the journal Proceedings of the Royal Society B and believe the specimen is a species called Posidonia australis. The giant plant is even larger than Pando, a clone colony of the American Aspen in Fishlake National Forest in Utah, USA, which was previously thought to be the largest plant in the world.
The West Australian seagrass that has now been examined is also home to a large variety of animals in its extent. Fish, crabs and turtles cavort between its leaves, but also larger mammals such as dolphins and manatees.
According to evolutionary biologist Elizabeth Sinclair, the scientists encountered the plant during a project to help them understand how genetically diverse the seagrass beds in Shark Bay are and which plants would be worth collecting offshoots for reclamation projects.
“We’re often asked how many different plants grow in seagrass beds,” she says. They would have wanted to find out with the help of genetic tools. That’s why the team collected seaweed sprouts from different places in Shark Bay and created a so-called “fingerprint” based on 18,000 genetic markers.
The answer “blew her away,” said Jane Edgeloe, a student at the University of Western Australia and the study’s lead author. “There was only one!” This meant that a single seaweed plant had spread over an area of 200 square kilometers.
The latter can be imagined a bit like a lawn that forms offshoots and thus takes up more and more space. In this way, the seagrass plant continued to expand over time – until it alone formed a gigantic seagrass meadow that is now larger than 28,000 football pitches. The researchers estimate that the plant must be at least 4,500 years old to reach this enormous extent.
During their study, the scientists from Adelaide came across another peculiarity: the unique plant seems to have twice as many chromosomes as its other relatives in the sea. That is, the plant received 100 percent of the genome from each parent, instead of the usual 50 percent.
According to the researchers, such plants are often found in places with extreme environmental conditions. The latter also applies to the plant’s home in Shark Bay. The salinity in the seawater there is twice as high as elsewhere in the bay and the water temperatures can fluctuate between 15 and 30 degrees Celsius.
Genetic studies of other seagrass species had already shown that the plants can live between 2,000 and 100,000 years, so the Shark Bay specimen’s age of 4,500 years is not unusual. “They have a versatile growth pattern,” Kathryn McMahon, a seaweed expert at Edith Cowan University in Western Australia who was not involved in the study, told the British Guardian.
This flexible growth pattern would contribute to the plants’ longevity, she said. Plants could grow toward nutrient-rich patches, gaps where they can spread further, or away from locations that are less suited to them.