Project 5.3 'Vulnerability of seagrass habitats in the Great Barrier Reef to flood plume impacts: light, nutrients, salinity'

Project 5.3 'Vulnerability of seagrass habitats in the Great Barrier Reef to flood plume impacts: light, nutrients, salinity'

Seagrass meadows are a vital habitat in tropical coastal ecosystems: they support biodiversity of estuarine, coastal and reef communities, including fisheries species, and they are a direct food source for obligate seagrass feeders such as dugongs. Seagrass meadows in the coastal zone also form a buffer between the catchment and the reef, trapping sediments and absorbing nutrients, with their high productivity rates facilitating rapid nutrient cycling. The Reef Rescue Marine Monitoring Program has identified that seagrass meadows along the GBR are in a state of decline (McKenzie et al. 2010).  Based on monitoring trends to June 2010, the indicators of this decline are: seagrass abundance reduced below subregional guidelines at 67% of sites, shrinking meadow area at 50% of sites, many sites having limited or are no production of seeds that would enable rapid recovery, indications of light limitation at 63% of sites, nutrient enrichment at 33% sites and high or elevated nitrogen at 90% of sites. There is also evidence of long-term increases of seagrass-tissue nutrients in coastal and reef seagrasses, particularly in the Wet Tropics and Burdekin regions. In addition, widespread impacts from flooding and cyclones occurred throughout the Great Barrier Reef in the summer 2010-2011, causing further declines in an already fragile system. The trends in seagrass decline, apart from the direct impact of tropical cyclones, are the result of changing water quality, particularly caused by the direct and indirect effects of flood plumes.

One of the biggest threats to seagrass meadow health is low light levels, particularly chronic low light levels, and pulsed acute low light that occurs as a result of flood plumes (Collier & Waycott 2009, Waycott et al. 2009). As such, light has, and is continuing to be, the focus of considerable research and monitoring over the last few years. We are now in a good position to explore interactive effects of low light with other water quality impacts, particularly features of water quality under flood plume conditions including high nutrients and low salinity. This two-year project will explore exposure of seagrass meadows to light, nutrients and salinity, seagrass responses to the interactive effects of these water quality impacts and contribute to the development of thresholds, the establishment of fundamental biological traits for input into modelling exercises and to biodiversity assessments.

Project objectives at a glance

In Year 1 of this project, researchers aim to:

  • Quantify exposure (duration and level of exposure) of seagrass meadows to light, nutrients and salinity impacts in flood plumes, by incorporating a temporal component to remote sensing and water type data.
  • Synthesise existing data on light, nutrients and salinity impacts to seagrass meadows, thresholds of response and evaluate knowledge gaps on seagrass responses to their interactive effects.
  • Measure the effects of changes in salinity on seagrass productivity and establish baseline salinity thresholds for input into future interactive studies.
  • Begin experiments on responses of coastal seagrass species to interactive effects of light, nutrients and salinity.

Specific objectives and intended outputs of this Project are detailed in the NERP TE Hub Multi-Year Research Plan.

Final Report

Final report on thresholds and indicators of declining water quality as tools for tropical seagrass management

Project Factsheet

Project Updates

See May 2012 Project Highlights here.


Link to the Project 5.3 homepage on e-Atlas



Project Duration: 
1 Jul 2011 to 31 Dec 2014


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Project Outputs