Scientists discover seagrass grows better after its seeds have been eaten by dugongs, turtles

It can take up to two weeks for seagrass seeds to pass through a dugong's digestive system. (Flickr: Julien Willem)

Dugongs and turtles can now be considered birds of the sea, as new research shows they play an incredible role in the growth of seagrass.

Researchers from James Cook University found seagrass seeds that had passed through the animals' digestive systems germinated much faster than those dropped by the grass.

Lead researcher Samantha Tol said the research involved sifting through hundreds of samples of dugong and turtle poo, collected from various locations along the Far North Queensland coast.

Dr Tol said they ended up scooping most of their samples from Gladstone Harbour and Cleveland Bay in Townsville.

Dr Tol and her team collected samples of turtle and dugong poo along the coast. (Supplied: TropWATER)

On their first day on the ocean, it took six hours to find the first poo, but on other days the researchers were much more successful.

"The very last day that we went out and harvested them, we found over 150 in about one-and-a-half to two hours," she said.

"That was in Cleveland Bay, in Townsville, and we were surrounded by 150, potentially 200, dugongs that were just happily popping up out of the water and feeding around us.

Dr Tol said the faecal samples were then taken back to the lab in an esky.

"I wouldn't recommend that if you want to keep using the esky in the future," she said.

Dugong and turtle poos float on the sea surface and are hard to distinguish from one another without testing DNA. (Supplied: TropWATER)

Under a microscope

Back at the lab, researchers then searched for the tiny seagrass seeds under a microscope.

They tested if the seeds were still viable and some were also planted, in the same conditions as other seeds taken from the seagrass plants.

By sifting through the many samples, Dr Tol said, she found most of the poos carried around one to two viable seeds for every gram of faeces.

Green turtles are among several species that eat seagrass along Queensland's coast. (Supplied: TropWATER)

The most exciting result, according to Dr Tol, was that the seeds that had been through a mega-herbivore's digestive system, germinated up to 60 per cent faster than those dropped straight from the plant.

"And the number of them that was germinating was four times greater."

Without an animal's intervention, Dr Tol said, usually seagrass seeds just dropped from the plant, often not moving very far and usually stay dormant for many months.

"These animals are eating in a meadow and because it takes them six to 14 days to digest their food, they can move quite a big distance between that time.

Seagrass is common along Queensland's east coast, including in meadows like these at Green Island near Cairns. (Supplied)

"They then let go of that seed in a non-glamorous fashion and that seed can now drop to the sea floor and instantly turn into a new plant."

She said this kind of seed dispersal could be a crucial element in maintaining and re-establishing seagrass beds.

So much more to discover

Dr Tol said it was incredibly exciting to make this breakthrough, especially considering the huge deficit in knowledge of seagrass habitats compared to other land and marine ecosystems.

"It's kind of like it was an unloved plant, not too many people were concerned with it," she said.

Dugongs are now thought to play a significant role in maintaining healthy seagrass ecosystems. (Supplied: Ahmed Skawky)

"I guess, maybe, the coral and the mangroves [got more attention] because they're so much more obvious got a little more of the attention.

"Now seagrass is finally getting its catch-up. Unfortunately, we're still behind, but that's also the fun part for a scientist."