Researchers from the University of Western Australia said that the seagrass meadow is in fact one single plant that covers around 180 sq km, or around three times the size of Manhattan. The plant was discovered at Shark Bay which lies approximately 800km north of Perth.
The research team initially collected seaweed samples and examined 18,000 genetic markers of the Posidonia australis, or ribbon weed, meadows to understand the genetic diversity and find out how many plants made up the meadow. The discovery therefore came much as a surprise, as Jane Edgeloe, lead author of the related study, published in the the journal Proceedings of the Royal Society B, says: “The answer blew us away – there was just one! That’s it, just one plant has expanded over 180km in Shark Bay, making it the largest known plant on Earth.”
As the species tends to grow around 35cm annually, the researchers believe that the plant spread from one tiny seed over 4,500 years ago.
Shark Bay seems like the perfect place for the species, according to the research team. “Shark Bay is a pretty unique environment which is largely undisturbed and has remained that way for some time, leading to its listing as a World Heritage Site. It is largely protected from the ocean which provides a fairly calm environment for the plant to keep growing. This could help explain why the clone is so big. It’s possible there is a larger one out there, as there is a lot we don’t know about our natural world,” says out Dr Elizabeth Sinclair, co-author of the study.
Despite the sheltered location, another factor might play a crucial role: the plant’s genetics. It reproduces by cloning and the research team established that it is a polyploid organism. These are known to have double the normal number of chromosomes.
Sinclair explains: “Diploid organisms, like you and me, only inherit half of their parents’ genome, whereas this seagrass has all of it. We suspect that this gives the plant an advantage over a diploid organism as it has all of the genes that help it survive in its current environment, as well as more genes which could help it survive in others. Reproducing clonally ensures the seagrass keeps the same genetics, as sexual reproduction in a diploid organism leads to new combinations of genes. While some will lead to new adaptations and an advantage, others will put it at a disadvantage.”
After making the exciting discovery, the researchers want to find out more about the plant’s resilience to climate change. A marine heatwave in 2010 and 2011 damaged 36% of seagrass meadows in Shark Bay but the seagrass is recovering and doing well, as Edgeloe points out: “As this clonal seagrass survived the marine heatwave and has been recovering since then, it looks promising, and perhaps the merging of its parental genomes has made it more resilient to climate change.”
“However, there is a climate threshold. We’ve set up monitoring experiments within and outside Shark Bay to try and figure out this threshold, and to see how Shark Bay’s organisms will react.”
“Shark Bay supports megafauna such as dugongs, turtles and dolphins as well as thousands of fish species. When the seagrass is affected by climate change, all of the animals at a higher trophic level are affected.”
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Photography courtesy of Ocean Image Bank / Ben Jones.