A team of CSIRO and UWA researchers has just returned from a 10-day field trip to Bardi Jawi country, where they took the last of their seagrass, seaweed and microalgae measurements for a WAMSI project that will determine the current state of the area’s primary food source for rabbitfish and green sea turtles.

The team worked with the Bardi Jawi Rangers on Tallon Island (Jalarn) and Sunday Island (Iwany) off the Dampier Peninsular in the Kimberley. They measured the growth of seagrass and macroalgae on the reef platforms, and microalgae in the sand that forms the beaches. These are all primary producers that sustain food webs, and the area’s seagrass is a key food source for fish and turtles that are important for the Bardi Jawi.

Preparing for seagrass tethering study (Mat Vanderklift)

Some seagrass was punched with holes to measure growth — researchers measure how far the holes have moved after a week to see how much the grass has grown. Other seagrass was collected, pegged out, measured and returned to the seagrass meadow for a 24 hour period before being measured again to determine how much had been eaten.

CSIRO’s Mat Vanderklift, who is also working on green sea turtle tagging as part of another WAMSI project, said the findings were providing the first comprehensive picture of productivity and seasonality of seaweed, seagrasses and microalgae in the Kimberley.

“Through collaboration with the Bardi Jawi Rangers we have been able to build up detailed seasonal understanding of seagrass productivity through the year,” Dr Vanderklift said. “We also have a better understanding of the importance of this productivity for green turtles and herbivorous fish like rabbitfish.”

Seagrass habitat with a sea cucumber in the Bardi Jawi IPA (Mat Vanderklift)

“The key findings are that the main plants that we have found in the lagoon habitats (the seagrasses Thalassia and Enhalus, and the large brown algae Sargassum) all have high growth rates throughout the year, with growth rates sometimes exceeding a centimetre a day,” Dr Vanderklift said. “We have also found that microscopic algae are very abundant in some places, but not everywhere, and bacteria are particularly abundant in the sediment under mangroves and seagrasses.”

The project has found that herbivores are abundant in the area and that they eat a lot of the seagrass. One of the main herbivores in the area, rabbitfish (Siganus lineatus), is a highly sought after food source by the Bardi Jawi people.

The project is also finding that the seagrasses are living at the limit of their temperature tolerances and further studies of their vulnerability to climate change are needed.

James McLaughlin on Jologo beach talking about microalga with kids from One Arm Point Remote Community School. (Mat Vanderklift)

“Collaborations with the Bardi Jawi Rangers have added enormous value to the research,” Dr Vanderklift said. “We have been able to exchange knowledge and learn from each other – for example, the discovery of the importance of seagrass to rabbitfish would not have happened if we had not worked closely together. The success of this project is because of the collaboration we have built together.”

The latest trip also gave the researchers an opportunity to present to children from the local One Arm Point Remote Community School.

James McLaughlin wowed the high school “Bush Rangers” with real-life chemistry on the beach, while Mat Vanderklift talked to dozens of excited children about turtles at their Culture Day. “They all enjoyed the game of guessing where the tagged turtles had travelled,” he said.

The project group is now completing the measurements and analysing the data, and will return to show the community and the rangers the results next year, with the aim of informing the ranger’s activities under their Indigenous Protected Area management plan.

Josh Setting up Benthic chamber module. (Mat Vanderklift)

 

 

The $30 million Kimberley Marine Research Program is funded through major investment supported by $12 million from the Western Australian government’s Kimberley Science and Conservation Strategy co-invested by the WAMSI partners and supported by the Traditional Owners of the Kimberley.

Kimberley Marine Research Program