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Seagrass keeps oceans alive and always leaves in time for summer!

18 July, 2019

We all swim a little faster over the seagrass to get to the white sand gleaming in Geographe Bay’s stunning clear water in summer, and then tiptoe around the piles of it lining the beaches in winter. While it may seem a nuisance at times, it is key to a healthy Bay.

Seagrasses are the only group of flowering plants that have adapted to the marine environment. Of the almost 60 species of seagrass, the strapweed Posidonia australis,is dominant in Geographe Bay. It is one of the dominant meadow-forming species found across temperate Australia, often within protected coastal bays and estuaries.

Seagrasses are amazing plants in that they:

  • Have leaves, roots and rhizomes, as well as flowers, fruits and seeds for reproduction;
  • Are “holobionts” – meaning that they each play host to a range of microorganisms such as bacteria, fungi and microalgae that help to support their health and survival;
  • Keep waterborne pathogens in check and neutralise harmful bacteria, keeping coral reefs healthy, and acting as an important part of the ocean’s well-being;
  • Provide a nursery for juvenile fish and crustaceans such as the Blue Swimmer Crab;
  • Provide food for a wide range of grazers, from dugongs to the green sea turtle, which feed on seagrass meadows;
  • Provide food for other marine animals that feed on the algae, fungi and bacteria it hosts;
  • Stabilise the ocean floor to prevent erosion;
  • Cycle nutrients; and
  • Produce oxygen.

And, for a final take home message, seagrasses are “blue carbon sinks”, storing huge amounts of organic carbon that would otherwise contribute enormously to the greenhouse effect. Researchers have calculated seagrass meadows could store 19.9 gigatonnes of organic carbon worldwide. In Geographe Bay, our seagrass meadows store a whopping $83M worth of carbon!

Next time you see seagrass washed up along the shores of Geographe Bay remember that we rely on a healthy ocean, and that the ocean is not healthy without seagrass.

This information was sourced from Hurtado-McCormick, V. Eelgrass keeps the oceans alive and preserves shipwrecks, so just cope when it tickles your feet. The Conversation: Beating Around the Bush, 2019. Available: