Vulnerability of seagrass habitats in the Great Barrier Reef to flood plume impacts: light, nutrients, salinity

Project 5.3

Project Leaders: Catherine Collier, Michelle Devlin and Jorge Alvarez-Romero - JCU

Seagrass meadows are a vital habitat in tropical coastal ecosystems but along the GBR they are in a state of decline. Recent mapping from this NERP project has shown the extent of seagrass exposed to flood plume pollutants (see graph). 

The project, which is exploring exposure of seagrass meadows to light, nutrients and salinity has also been able to show threshold levels of light associated with seagrass loss by measuring fluctuations in seagrass abundance at three-monthly intervals over three years.

One of the biggest threats to seagrass meadow health is low light levels that occur as a result of flood plumes. With colleagues from Edith Cowan University, the researchers have conducted a global analysis of seagrass responses to light reduction with the aim of identifying robust and consistent indicators, which can be recommended to environmental managers for monitoring.

In a trial to test tolerance to reduced salinity, three common seagrass species along GBR coasts and estuaries are showing very broad salinity tolerance. However, in two species this initial tolerance in the first few weeks was later followed by mortality at very low salinities. The trial will be completed in early May.

In the next stage of the project, changes in seagrass meadow area will be matched against water quality measurements to test whether declines in water quality were the primary cause of meadow loss throughout the GBR since 2008.

The researchers will also soon be testing how nutrient availability can modify light thresholds, e.g. where nutrients are limited, do plants have higher light requirements? They also want to investigate whether nutrient availability changes the sensitivity of the indicators they are testing.

Contact: Catherine Collier

See more information about this project here.