Plant Biology

Postgraduate research profiles

Matthew Fraser

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The role of sedimentary organic phosphorus in P supply to seagrass meadows of oligotrophic, coastal embayments


Phosphorus is an essential nutrient for seagrasses - a group of marine plants that are critical for healthy marine ecosystems. However, seagrasses often grow in nutrient-poor ecosystems, where inorganic phosphorus concentrations in both sediments and the water column are extremely low.

In terrestrial ecosystems with low phosphorus availabilities, the organic phosphorus pool in sediments can provide plants with the majority of their phosphorus requirements. However, we do not know if the organic phosphorus pool is an important source of phosphorus in seagrass ecosystems. In particular, microbes drive changing phosphorus availabilities through processes such as mineralization and immobilization in most ecosystems, yet are extremely understudied in seagrass sediments. I will determine the role of the organic phosphorus pool and microbes in supplying phosphorus to seagrasses growing in Shark Bay; a World Heritage Site with abundant seagrasses and extremely low phosphorus concentrations.

Why my research is important

Seagrasses are the dominant benthic producers in Shark Bay, and contribute significantly to Shark Bay’s biodiversity and status as a World Heritage Site. For example, seagrasses indirectly contribute to the diet of charismatic megafauna such as tiger sharks and sea turtles. In addition, seagrass sediments have also been identified as potential sinks of atmospheric carbon, with Shark Bay seen as a global hotspot of coastal CO2 sequestration. However, seagrasses in nutrient poor embayments are susceptible to changes in phosphorus concentrations, and the greatest threat to seagrasses in Shark Bay appears to be from predicted increases in phosphorus inputs. We can only fully protect seagrasses from these threats when we fully understand the phosphorus cycle in seagrass sediments, which my research will contribute to.


  • Australian Postgraduate Award
  • UWA Safety Net Top-Up Scholarship
  • Caring for our Country Grant
  • John Leslie & Dorise Barron Memorial Post-Graduate Grant
  • 2013 Hodgkin Trust Scholarship

Seagrasses maintain high biodiversity in critical marine ecosystems