NT seagrass study finds huge meadows

·3-min read

Marine seagrass meadows in waters off the Northern Territory are more widespread and diverse than previously thought, new research has found.

The first survey in 15 years of the Limmen Marine Park and the Limmen Bight Marine Park in the Gulf of Carpentaria found eight seagrass species growing in shallow water to a depth of 20 metres.

They provide critical habitat for vulnerable dugong and turtle populations as well as fish, crabs and other marine species.

Marine biologist Rachel Groom said the study added to the knowledge about migratory and threatened species that rely on seagrass habitats.

"We found seagrass in the lower reaches of the coastal creeks, not just the intertidal areas. It was more extensive than formerly documented," Dr Groom said.

"We are now mapping and describing the seagrass habitats that underpin ecosystem."

The 2250 sq km survey was conducted over two weeks using helicopters to map sea floor habitats exposed at low tide and boats for deeper waters.

Marine biologist Alex Carter said the team had surveyed more than 3000 seagrass sites across Marra and Yanyuwa Indigenous sea country.

"This is by far the most detailed seagrass survey in the southern Gulf. We expected quite patchy seagrass and perhaps four or five species," she said.

"What we found were continuous meadows that extended from very shallow sandbanks next to mangroves that exposes at low tide, to deep meadows down to 20 metres at the edge of the marine park," she said.

Dr Carter said the species were found in different habitats within the survey area and the height of the seagrass canopy exceeded expectations in some areas.

"Very dense seagrass also extended up into coastal creeks, which is unusual to see," she said.

But it is not all good news for the Gulf's seagrass meadows and the species that rely on the them.

Climate change is causing the Gulf's sea surface temperature to rise, which in turn is increasing the amount and intensity of storm activity, including destructive cyclones.

"Lush seagrass meadows can rapidly deteriorate by shedding leaves and eventually shrinking in area when faced with extreme weather," ecophysiologist Catherine Collier said.

"Climate impacts could also reduce the resilience of seagrass habitats and increase their vulnerability to other threats."

Such habitat loss would have flow-on effects for species that rely on seagrass for food and shelter.

"Any seagrass decline is likely to have severe, negative effects on dugong and turtles,' Dr Groom said.

"They will both delay breeding if seagrass habitats decline."

The research is a collaboration between Mabunji li-Anthawirriyarra Land and Sea Rangers, James Cook University and Charles Darwin University scientists, and the NT Parks and Wildlife Commission.

Senior li-Anthawirriyarra sea ranger Shaun Evans said the mapping project was important for setting a foundation for future seagrass monitoring.

"We need to know what resources we have and where they are located," he said.

"These habitats support turtle, dugong and fish that are significant to Marra and Yanyuwa people, knowing they are healthy is important for us".

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