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Keep Watch Seagrass Monitoring

The Geographe Bay “Keep watch” seagrass monitoring program was developed in partnership with Edith Cowan University in 2012.

The aim of the program is to establish a long-term monitoring program to assess the health of seagrasses in Geographe Bay. 

Geographe Bay supports the most extensive seagrass meadows in temperate Western Australia, which store more than $83 million worth of carbon.  The meadows also provide many important ecological functions that makes them vital to the ecosystem of Geographe Bay.

Predicted increases in nutrients off the catchment have the potential to impact on the health of Geographe Bay seagrass meadows by enhancing the growth of epiphytes and algae which grow on or in the water column above seagrass, reducing light necessary for growth. 

Annual seagrass monitoring has occurred since 2012 at eight sites within Geographe Bay.  Shoot density of the dominant seagrass species Posidonia sinuosa, tissue nutrients, algal epiphyte cover (indicative of poor water quality) and water quality parameters are monitored annually to assess changes in seagrass health.  Tissue nutrients are also analysed for Amphibolis Antarctica, another dominant seagrass species, at three sites including Capel, where Posidonia sinuosa does not occur. 

The project is coordinated by GeoCatch with monitoring by Edith Cowan University and the Department of Biodiversity, Conservation and Attractions with financial support from the Water Corporation.

Key findings to date:

  • Seagrass meadows in Geographe Bay remain healthy with seagrass shoot densities high at all sites.
  • Shoot densities increased at all sites from 2024, and were at an all time high in 2025 compared to other years, and other regions.
  • Highest shoot densities were recorded at Buayanyup and Busselton Jetty, with lowest at the Vasse-Wonnerup and Vasse Diversion.
  • No management triggers were breached in 2025.
  • The epiphyte cover declined from previous years. The dominant epiphyte types remain microalgal accumulations which are not the type commonly associated with nutrient enrichment.
  • Nutrient content of seagrasses in Geographe Bay continues to be low with signs of higher exposure at Capel. The higher nitrogen isotope signal at Capel suggests that nitrogen derived from animal wastes, septic tanks or from natural vegetation is also a main source.

Keep Watch annual seagrass monitoring will continue until 2026 through funding from the Water Corporation.

The latest Keep Watch Seagrass monitoring report is available here.