Queensland scientists brave crocodiles and deadly jellyfish to regrow seagrass

Researchers have been forced to avoid crocodiles, deadly jellyfish and even quicksand-like mud to replant seagrass beds south of Cairns as part of a project they hope to expand across tropical Australia.

The underwater meadows at Mourilyan Harbour were once thriving habitats, providing food for prawns, dugongs and green sea turtles.

But the three hectare-site was destroyed more than a decade ago by a series of La Niña events, including Cyclone Larry, and the sand banks it needed to regrow washed away.

“This was a case where we absolutely needed intervention for the grasses to come back,” Associate Professor Michael Rasheed said. “We were really concerned, this is never going to come back unless we help.”

The James Cook University team this week ventured into the harbour in small boats and released seagrass plants anchored to frames, sinking them to the seabed.

“We can’t get in the water to do this work because there are lots of big crocs about and stingers,” Rasheed said.

Crocodile sightings aren’t unknown and there are other challenges too, with the seabed made of a quicksand-like sediment that’s exposed at low tide.

Daar is 15 species of seagrass that live on the Great Barrier Reef but scientists don’t yet know how to help them recover from damage and it’s hoped the project will be a blueprint for restoring these environments.

“People usually think of coral on the Great Barrier Reef but there’s actually more seagrass than coral,” Rasheed said.

As well as providing a nursery for many different species, seagrass meadows are also effective carbon sinks – more than 30 times better at removing carbon dioxide from the atmosphere than tropical rainforests.

According to Rasheed, that makes them a potential weapon against climate change.

They can also filter out the nutrients and deal with the sediment flowing into tropical Queensland waters that are damaging the reef.

Early trials in 2020 found the seagrass grew on steel frames but these were not a long-term solution and the team is instead trying out biodegradable matting made from potato starch.

The researchers monitor how the seagrass is growing by flying drones over the site when the tide is low and taking high-resolution photos.

The project, run with volunteers and Indigenous rangers, is looking for more funding to rehabilitate meadows across tropical Australia and the Pacific.

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