Fish and turtles can, at times, consume all of the growth of the seagrasses: that’s among the findings of a three-year study that has combined science and traditional knowledge to investigate the productivity of seagrasses and other marine plants, and how important this is for the animals of the Kimberley region.

Researchers from CSIRO, The University of Western Australia (UWA) and Edith Cowan University teamed  up with the Bardi Jawi Rangers – who look after more than 250 kilometres of coast and the 340,700-hectare Bardi Jawi Indigenous Protected Area.

The Western Australian Marine Science Institution (WAMSI) project team, including UWA’s Professor Gary Kendrick and CSIRO’s Dr Mat Vanderklift, spent three years studying the seagrasses and macroalgae (large seaweed) that grow on the seafloor along the coast and islands around One Arm Point.

Monitoring seagrass growth is very important to assess stress levels and their resilience to change.

The main plants found in the lagoon habitats by the team were the seagrasses Thalassia (also called turtlegrass) and Enhalus, and the large brown algae Sargassum.

These seagrasses are living at extremes in both temperature oxygen levels (high oxygen during the day and low oxygen during the night), and are under threat from climate change.

All of these plants have high growth rates throughout the year, sometimes exceeding a centimetre a day.

However, the research also found that seasonally variable grazing by a range of large vertebrate herbivores, like fish and turtles can consume all of the growth of the seagrasses.

Microscopic algae were very abundant in some places, but not everywhere, and bacteria were particularly abundant in the sediment under mangroves and seagrasses.

The team discovered that herbivores were abundant and ate a lot of the seagrass.

One of the main herbivores was the rabbitfish (Siganus lineatus) which is also a highly sought after food source for the Bardi Jawi people. Green turtles were also abundant, moving at high tide onto the seagrass beds.

Collaborations with the Bardi Jawi Rangers, who are custodians of the Indigenous Protected Area, added enormous value to the research. The exchange of knowledge with the rangers during the project recognised the importance of seagrass to rabbitfish. Therefore, the research concludes, marine park plans should consider these as Key Performance Indicators.

Bardi Jawi ranger Dwayne George and researcher Monique Grol measuring seagrass growth (Monique Grol)

“Particular care should be taken to ensure that the habitats that contain these plants are not degraded, and are monitored in a way that will ensure that any change — even small — is detected,” Professor Kendrick said.

Some work is still needed to develop methods for monitoring that will work in the Kimberley, and that can be adopted and applied by Indigenous ranger groups for Healthy Country Plan monitoring.

Links:

• Benthic primary productivity_WAMSI KMRP Project 2.2.4_Kendrick et al 2017_Final
• Project page: WAMSI KMRP project 2.2.4 Seagrass

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

Kimberley Marine Research Program